The STMQ framework is an object-oriented API for integrating Message Queues with Objective-C code. It is mainly intended to allow the addition of concurrency easily by use of Active Objects to create Actors with Futures. Additional work is being done to eventually support messaging between different processes and different systems (mainly via AMQP).
STMQ is largely based on Apple’s Foundation objects, such as NSProxy and NSOperationQueue. It is implemented in such a way that you can easily add multi-threaded execution to existing code (or remove it) without having to do excessive restructuring of your implementation.