We consider the problem of implementing multiway synchronization in a distributed environment providing only binary asynchronous communication. Our implementation strategy is formulated as a transformation on transition systems and we give a distributed algorithm for multiway synchronization. Correctness assertions and proofs are based on a new method: coupled simulations. The coupled simulation equivalence is weaker than observation equivalence and stronger than testing equivalence and combines some of their advantages. Like observation equivalence (and unlike testing) it is established through case analysis over single transitions. Like testing equivalence (and unlike observation) it allows an internal choice to be distributed onto several internal choices. The latter is particularly important when relating our distributed implementations to their specifications.