Ever since the publication of Enterprise Integration Patterns people have been using the notation introduced in that book for documenting asynchronous heterogenous messaging systems.
But our shop is more or less standardized around a proprietary documentation tool that does exclusively UML. Is one of the standard UML diagrams appropriate for documenting asynchronous messaging systems, including transformers, routers et al.? If yes, which one? If not, what would be a killer argument against the tweaking of UML for this purpose?