looking for other distributed debuggers

I've been working on Causeway to make it more generally useful to
developers debugging asynchronous message-passing programs. This
effort includes writing a paper, which I'm considering submitting
here:

http://debs08.dis.uniroma1.it/

Here's a link to the draft paper, which is pretty rough, only half written.

http://www.erights.org/elang/tools/causeway/causeway-paper.pdf

Trying to write the Related Works section has been pretty frustrating.
Can anyone point me at debuggers built for the communicating event
loops concurrency model?

Thanks,
Terry