diff --git a/IPython/zmq/parallel/client.py b/IPython/zmq/parallel/client.py
index 673f82f..ae1cbcb 100644
--- a/IPython/zmq/parallel/client.py
+++ b/IPython/zmq/parallel/client.py
@@ -2,19 +2,17 @@
 """A semi-synchronous Client for the ZMQ controller"""
 
 import time
-import threading
 
 from pprint import pprint
 
-from functools import wraps
-
 from IPython.external.decorator import decorator
 
 import streamsession as ss
 import zmq
-
+from zmq.eventloop import ioloop, zmqstream
 from remotenamespace import RemoteNamespace
 from view import DirectView
+from dependency import Dependency, depend, require
 
 def _push(ns):
     globals().update(ns)
@@ -147,13 +145,13 @@ class Client(object):
         self.history = []
         self.debug = debug
         self.session.debug = debug
-        self._connect()
         
         self._notification_handlers = {'registration_notification' : self._register_engine,
                                     'unregistration_notification' : self._unregister_engine,
                                     }
         self._queue_handlers = {'execute_reply' : self._handle_execute_reply,
                                 'apply_reply' : self._handle_apply_reply}
+        self._connect()
         
     
     @property
@@ -453,7 +451,8 @@ class Client(object):
         result = self.apply(execute, (code,), targets=None, block=block, bound=False)
         return result
     
-    def _apply_balanced(self, f, args, kwargs, bound=True, block=None):
+    def _apply_balanced(self, f, args, kwargs, bound=True, block=None,
+                            after=None, follow=None):
         """the underlying method for applying functions in a load balanced
         manner."""
         block = block if block is not None else self.block
@@ -471,17 +470,29 @@ class Client(object):
         else:
             return msg_id
     
-    def _apply_direct(self, f, args, kwargs, bound=True, block=None, targets=None):
+    def _apply_direct(self, f, args, kwargs, bound=True, block=None, targets=None,
+                                after=None, follow=None):
         """Then underlying method for applying functions to specific engines."""
+        
         block = block if block is not None else self.block
+        
         queues,targets = self._build_targets(targets)
         print queues
         bufs = ss.pack_apply_message(f,args,kwargs)
+        if isinstance(after, Dependency):
+            after = after.as_dict()
+        elif after is None:
+            after = []
+        if isinstance(follow, Dependency):
+            follow = follow.as_dict()
+        elif follow is None:
+            follow = []
+        subheader = dict(after=after, follow=follow)
         content = dict(bound=bound)
         msg_ids = []
         for queue in queues:
             msg = self.session.send(self.queue_socket, "apply_request", 
-                    content=content, buffers=bufs,ident=queue)
+                    content=content, buffers=bufs,ident=queue, subheader=subheader)
             msg_id = msg['msg_id']
             self.outstanding.add(msg_id)
             self.history.append(msg_id)
@@ -501,7 +512,8 @@ class Client(object):
                     result[target] = self.results[mid]
             return result
     
-    def apply(self, f, args=None, kwargs=None, bound=True, block=None, targets=None):
+    def apply(self, f, args=None, kwargs=None, bound=True, block=None, targets=None,
+                        after=None, follow=None):
         """calls f(*args, **kwargs) on a remote engine(s), returning the result.
         
         if self.block is False:
@@ -509,17 +521,22 @@ class Client(object):
         else:
             returns actual result of f(*args, **kwargs)
         """
+        # enforce types of f,args,kwrags
         args = args if args is not None else []
         kwargs = kwargs if kwargs is not None else {}
+        if not callable(f):
+            raise TypeError("f must be callable, not %s"%type(f))
         if not isinstance(args, (tuple, list)):
             raise TypeError("args must be tuple or list, not %s"%type(args))
         if not isinstance(kwargs, dict):
             raise TypeError("kwargs must be dict, not %s"%type(kwargs))
+            
+        options  = dict(bound=bound, block=block, after=after, follow=follow)
+            
         if targets is None:
-            return self._apply_balanced(f,args,kwargs,bound=bound, block=block)
+            return self._apply_balanced(f, args, kwargs, **options)
         else:
-            return self._apply_direct(f, args, kwargs,
-                        bound=bound,block=block, targets=targets)
+            return self._apply_direct(f, args, kwargs, targets=targets, **options)
     
     def push(self, ns, targets=None, block=None):
         """push the contents of `ns` into the namespace on `target`"""
@@ -598,5 +615,26 @@ class Client(object):
         #     else:
         #         break
         return msg['content']
+
+class AsynClient(Client):
+    """An Asynchronous client, using the Tornado Event Loop"""
+    io_loop = None
+    queue_stream = None
+    notifier_stream = None
+    
+    def __init__(self, addr, context=None, username=None, debug=False, io_loop=None):
+        Client.__init__(self, addr, context, username, debug)
+        if io_loop is None:
+            io_loop = ioloop.IOLoop.instance()
+        self.io_loop = io_loop
+        
+        self.queue_stream = zmqstream.ZMQStream(self.queue_socket, io_loop)
+        self.control_stream = zmqstream.ZMQStream(self.control_socket, io_loop)
+        self.task_stream = zmqstream.ZMQStream(self.task_socket, io_loop)
+        self.notification_stream = zmqstream.ZMQStream(self.notification_socket, io_loop)
     
+    def spin(self):
+        for stream in (self.queue_stream, self.notifier_stream, 
+                        self.task_stream, self.control_stream):
+            stream.flush()
     
\ No newline at end of file
diff --git a/IPython/zmq/parallel/dependency.py b/IPython/zmq/parallel/dependency.py
index 98a2cd2..7f2a8a8 100644
--- a/IPython/zmq/parallel/dependency.py
+++ b/IPython/zmq/parallel/dependency.py
@@ -50,6 +50,55 @@ class dependent(object):
             raise UnmetDependency()
         return self.f(*args, **kwargs)
 
+def _require(*names):
+    for name in names:
+        try:
+            __import__(name)
+        except ImportError:
+            return False
+    return True
 
-__all__ = ['UnmetDependency', 'depend', 'evaluate_dependencies']
+def require(*names):
+    return depend(_require, *names)
+
+class Dependency(set):
+    """An object for representing a set of dependencies.
+    
+    Subclassed from set()."""
+    
+    mode='all'
+    
+    def __init__(self, dependencies=[], mode='all'):
+        if isinstance(dependencies, dict):
+            # load from dict
+            dependencies = dependencies.get('dependencies', [])
+            mode = dependencies.get('mode', mode)
+        set.__init__(self, dependencies)
+        self.mode = mode.lower()
+        if self.mode not in ('any', 'all'):
+            raise NotImplementedError("Only any|all supported, not %r"%mode)
+    
+    def check(self, completed):
+        if len(self) == 0:
+            return True
+        if self.mode == 'all':
+            for dep in self:
+                if dep not in completed:
+                    return False
+            return True
+        elif self.mode == 'any':
+            for com in completed:
+                if com in self.dependencies:
+                    return True
+            return False
+    
+    def as_dict(self):
+        """Represent this dependency as a dict. For json compatibility."""
+        return dict(
+            dependencies=list(self),
+            mode=self.mode
+        )
+    
+
+__all__ = ['UnmetDependency', 'depend', 'require', 'Dependency']
 
diff --git a/IPython/zmq/parallel/scheduler.py b/IPython/zmq/parallel/scheduler.py
new file mode 100644
index 0000000..8d2e388
--- /dev/null
+++ b/IPython/zmq/parallel/scheduler.py
@@ -0,0 +1,401 @@
+#----------------------------------------------------------------------
+# Imports
+#----------------------------------------------------------------------
+
+from random import randint,random
+
+try:
+    import numpy
+except ImportError:
+    numpy = None
+
+import zmq
+from zmq.eventloop import ioloop, zmqstream
+
+# local imports
+from IPython.zmq.log import logger # a Logger object
+from client import Client
+from dependency import Dependency
+import streamsession as ss
+
+from IPython.external.decorator import decorator
+
+@decorator
+def logged(f,self,*args,**kwargs):
+    print ("#--------------------")
+    print ("%s(*%s,**%s)"%(f.func_name, args, kwargs))
+    return f(self,*args, **kwargs)
+
+#----------------------------------------------------------------------
+# Chooser functions
+#----------------------------------------------------------------------
+
+def plainrandom(loads):
+    """Plain random pick."""
+    n = len(loads)
+    return randint(0,n-1)
+
+def lru(loads):
+    """Always pick the front of the line.
+    
+    The content of loads is ignored.
+    
+    Assumes LRU ordering of loads, with oldest first.
+    """
+    return 0
+
+def twobin(loads):
+    """Pick two at random, use the LRU of the two.
+    
+    The content of loads is ignored.
+    
+    Assumes LRU ordering of loads, with oldest first.
+    """
+    n = len(loads)
+    a = randint(0,n-1)
+    b = randint(0,n-1)
+    return min(a,b)
+
+def weighted(loads):
+    """Pick two at random using inverse load as weight.
+    
+    Return the less loaded of the two.
+    """
+    # weight 0 a million times more than 1:
+    weights = 1./(1e-6+numpy.array(loads))
+    sums = weights.cumsum()
+    t = sums[-1]
+    x = random()*t
+    y = random()*t
+    idx = 0
+    idy = 0
+    while sums[idx] < x:
+        idx += 1
+    while sums[idy] < y:
+        idy += 1
+    if weights[idy] > weights[idx]:
+        return idy
+    else:
+        return idx
+
+def leastload(loads):
+    """Always choose the lowest load.
+    
+    If the lowest load occurs more than once, the first
+    occurance will be used.  If loads has LRU ordering, this means
+    the LRU of those with the lowest load is chosen.
+    """
+    return loads.index(min(loads))
+
+#---------------------------------------------------------------------
+# Classes
+#---------------------------------------------------------------------
+class TaskScheduler(object):
+    """Simple Python TaskScheduler object.
+    
+    This is the simplest object that supports msg_id based
+    DAG dependencies. *Only* task msg_ids are checked, not
+    msg_ids of jobs submitted via the MUX queue.
+    
+    """
+    
+    scheme = leastload # function for determining the destination
+    client_stream = None # client-facing stream
+    engine_stream = None # engine-facing stream
+    mon_stream = None # controller-facing stream
+    dependencies = None # dict by msg_id of [ msg_ids that depend on key ]
+    depending = None # dict by msg_id of (msg_id, raw_msg, after, follow)
+    pending = None # dict by engine_uuid of submitted tasks
+    completed = None # dict by engine_uuid of completed tasks
+    clients = None # dict by msg_id for who submitted the task
+    targets = None # list of target IDENTs
+    loads = None # list of engine loads
+    all_done = None # set of all completed tasks
+    blacklist = None # dict by msg_id of locations where a job has encountered UnmetDependency
+    
+    
+    def __init__(self, client_stream, engine_stream, mon_stream, 
+                notifier_stream, scheme=None, io_loop=None):
+        if io_loop is None:
+            io_loop = ioloop.IOLoop.instance()
+        self.io_loop = io_loop
+        self.client_stream = client_stream
+        self.engine_stream = engine_stream
+        self.mon_stream = mon_stream
+        self.notifier_stream = notifier_stream
+        
+        if scheme is not None:
+            self.scheme = scheme
+        else:
+            self.scheme = TaskScheduler.scheme
+        
+        self.session = ss.StreamSession(username="TaskScheduler")
+        
+        self.dependencies = {}
+        self.depending = {}
+        self.completed = {}
+        self.pending = {}
+        self.all_done = set()
+        
+        self.targets = []
+        self.loads = []
+        
+        engine_stream.on_recv(self.dispatch_result, copy=False)
+        self._notification_handlers = dict(
+            registration_notification = self._register_engine,
+            unregistration_notification = self._unregister_engine
+        )
+        self.notifier_stream.on_recv(self.dispatch_notification)
+    
+    def resume_receiving(self):
+        """resume accepting jobs"""
+        self.client_stream.on_recv(self.dispatch_submission, copy=False)
+    
+    def stop_receiving(self):
+        self.client_stream.on_recv(None)
+    
+    #-----------------------------------------------------------------------
+    # [Un]Registration Handling
+    #-----------------------------------------------------------------------
+    
+    def dispatch_notification(self, msg):
+        """dispatch register/unregister events."""
+        idents,msg = self.session.feed_identities(msg)
+        msg = self.session.unpack_message(msg)
+        msg_type = msg['msg_type']
+        handler = self._notification_handlers.get(msg_type, None)
+        if handler is None:
+            raise Exception("Unhandled message type: %s"%msg_type)
+        else:
+            try:
+                handler(str(msg['content']['queue']))
+            except KeyError:
+                logger.error("task::Invalid notification msg: %s"%msg)
+    @logged
+    def _register_engine(self, uid):
+        """new engine became available"""
+        # head of the line:
+        self.targets.insert(0,uid)
+        self.loads.insert(0,0)
+        # initialize sets
+        self.completed[uid] = set()
+        self.pending[uid] = {}
+        if len(self.targets) == 1:
+            self.resume_receiving()
+
+    def _unregister_engine(self, uid):
+        """existing engine became unavailable"""
+        # handle any potentially finished tasks:
+        if len(self.targets) == 1:
+            self.stop_receiving()
+        self.engine_stream.flush()
+        
+        self.completed.pop(uid)
+        lost = self.pending.pop(uid)
+        
+        idx = self.targets.index(uid)
+        self.targets.pop(idx)
+        self.loads.pop(idx)
+        
+        self.handle_stranded_tasks(lost)
+    
+    def handle_stranded_tasks(self, lost):
+        """deal with jobs resident in an engine that died."""
+        # TODO: resubmit the tasks?
+        for msg_id in lost:
+            pass
+    
+    
+    #-----------------------------------------------------------------------
+    # Job Submission
+    #-----------------------------------------------------------------------
+    @logged
+    def dispatch_submission(self, raw_msg):
+        """dispatch job submission"""
+        # ensure targets up to date:
+        self.notifier_stream.flush()
+        try:
+            idents, msg = self.session.feed_identities(raw_msg, copy=False)
+        except Exception, e:
+            logger.error("task::Invaid msg: %s"%msg)
+            return
+        
+        msg = self.session.unpack_message(msg, content=False, copy=False)
+        print idents,msg
+        header = msg['header']
+        msg_id = header['msg_id']
+        after = Dependency(header.get('after', []))
+        if after.mode == 'all':
+            after.difference_update(self.all_done)
+        if after.check(self.all_done):
+            # recast as empty set, if we are already met, 
+            # to prevent 
+            after = Dependency([])
+        
+        follow = Dependency(header.get('follow', []))
+        print raw_msg
+        if len(after) == 0:
+            # time deps already met, try to run
+            if not self.maybe_run(msg_id, raw_msg, follow):
+                # can't run yet
+                self.save_unmet(msg_id, raw_msg, after, follow)
+        else:
+            self.save_unmet(msg_id, raw_msg, after, follow)
+        # send to monitor
+        self.mon_stream.send_multipart(['intask']+raw_msg, copy=False)
+    @logged
+    def maybe_run(self, msg_id, raw_msg, follow=None):
+        """check location dependencies, and run if they are met."""
+            
+        if follow:
+            def can_run(idx):
+                target = self.targets[idx]
+                return target not in self.blacklist.get(msg_id, []) and\
+                        follow.check(self.completed[target])
+            
+            indices = filter(can_run, range(len(self.targets)))
+            if not indices:
+                return False
+        else:
+            indices = None
+            
+        self.submit_task(msg_id, raw_msg, indices)
+        return True
+            
+    @logged
+    def save_unmet(self, msg_id, msg, after, follow):
+        """Save a message for later submission when its dependencies are met."""
+        self.depending[msg_id] = (msg_id,msg,after,follow)
+        # track the ids in both follow/after, but not those already completed
+        for dep_id in after.union(follow).difference(self.all_done):
+            if dep_id not in self.dependencies:
+                self.dependencies[dep_id] = set()
+            self.dependencies[dep_id].add(msg_id)
+    @logged
+    def submit_task(self, msg_id, msg, follow=None, indices=None):
+        """submit a task to any of a subset of our targets"""
+        if indices:
+            loads = [self.loads[i] for i in indices]
+        else:
+            loads = self.loads
+        idx = self.scheme(loads)
+        if indices:
+            idx = indices[idx]
+        target = self.targets[idx]
+        print target, map(str, msg[:3])
+        self.engine_stream.socket.send(target, flags=zmq.SNDMORE, copy=False)
+        self.engine_stream.socket.send_multipart(msg, copy=False)
+        self.add_job(idx)
+        self.pending[target][msg_id] = (msg, follow)
+    
+    #-----------------------------------------------------------------------
+    # Result Handling
+    #-----------------------------------------------------------------------
+    @logged
+    def dispatch_result(self, raw_msg):
+        try:
+            idents,msg = self.session.feed_identities(raw_msg, copy=False)
+        except Exception, e:
+            logger.error("task::Invaid result: %s"%msg)
+            return
+        msg = self.session.unpack_message(msg, content=False, copy=False)
+        header = msg['header']
+        if header.get('dependencies_met', True):
+            self.handle_result_success(idents, msg['parent_header'], raw_msg)
+            # send to monitor
+            self.mon_stream.send_multipart(['outtask']+raw_msg, copy=False)
+        else:
+            self.handle_unmet_dependency(self, idents, msg['parent_header'])
+        
+    @logged
+    def handle_result_success(self, idents, parent, raw_msg):
+        # first, relay result to client
+        engine = idents[0]
+        client = idents[1]
+        # swap_ids for XREP-XREP mirror
+        raw_msg[:2] = [client,engine]
+        print map(str, raw_msg[:4])
+        self.client_stream.send_multipart(raw_msg, copy=False)
+        # now, update our data structures
+        msg_id = parent['msg_id']
+        self.pending[engine].pop(msg_id)
+        self.completed[engine].add(msg_id)
+        
+        self.update_dependencies(msg_id)
+        
+    @logged
+    def handle_unmet_dependency(self, idents, parent):
+        engine = idents[0]
+        msg_id = parent['msg_id']
+        if msg_id not in self.blacklist:
+            self.blacklist[msg_id] = set()
+        self.blacklist[msg_id].add(engine)
+        raw_msg,follow = self.pending[engine].pop(msg_id)
+        if not self.maybe_run(raw_msg, follow):
+            # resubmit failed, put it back in our dependency tree
+            self.save_unmet(msg_id, raw_msg, Dependency(), follow)
+        pass
+    @logged
+    def update_dependencies(self, dep_id):
+        """dep_id just finished. Update our dependency
+        table and submit any jobs that just became runable."""
+        if dep_id not in self.dependencies:
+            return
+        jobs = self.dependencies.pop(dep_id)
+        for job in jobs:
+            msg_id, raw_msg, after, follow = self.depending[job]
+            if msg_id in after:
+                after.remove(msg_id)
+            if not after: # time deps met
+                if self.maybe_run(msg_id, raw_msg, follow):
+                    self.depending.pop(job)
+                    for mid in follow:
+                        self.dependencies[mid].remove(msg_id)
+    
+    #----------------------------------------------------------------------
+    # methods to be overridden by subclasses
+    #----------------------------------------------------------------------
+    
+    def add_job(self, idx):
+        """Called after self.targets[idx] just got the job with header.
+        Override with subclasses.  The default ordering is simple LRU.
+        The default loads are the number of outstanding jobs."""
+        self.loads[idx] += 1
+        for lis in (self.targets, self.loads):
+            lis.append(lis.pop(idx))
+            
+    
+    def finish_job(self, idx):
+        """Called after self.targets[idx] just finished a job.
+        Override with subclasses."""
+        self.loads[idx] -= 1
+    
+
+
+def launch_scheduler(in_addr, out_addr, mon_addr, not_addr, scheme='weighted'):
+    from zmq.eventloop import ioloop
+    from zmq.eventloop.zmqstream import ZMQStream
+    
+    ctx = zmq.Context()
+    loop = ioloop.IOLoop()
+    
+    scheme = globals().get(scheme)
+    
+    ins = ZMQStream(ctx.socket(zmq.XREP),loop)
+    ins.bind(in_addr)
+    outs = ZMQStream(ctx.socket(zmq.XREP),loop)
+    outs.bind(out_addr)
+    mons = ZMQStream(ctx.socket(zmq.PUB),loop)
+    mons.connect(mon_addr)
+    nots = ZMQStream(ctx.socket(zmq.SUB),loop)
+    nots.setsockopt(zmq.SUBSCRIBE, '')
+    nots.connect(not_addr)
+    
+    scheduler = TaskScheduler(ins,outs,mons,nots,scheme,loop)
+    
+    loop.start()
+
+
+if __name__ == '__main__':
+    iface = 'tcp://127.0.0.1:%i'
+    launch_scheduler(iface%12345,iface%1236,iface%12347,iface%12348)