A prerelease of dramatis has gone up on http:://dramatis.mischance.net.

dramatis is an actor library for dynamic languages. It allows developers to
write concurrent programs using the actor model rather than having to code
against lower level thread APIs.

This prerelease of dramatis is implemented in Ruby (a Python port has
started) and runs on Ruby 1.8.6, Ruby 1.9, and recent JRuby 1.1.1 RCs (with
a very little bit of testing done against Rubinius). It was developed and
tested primarily on Linux and OS X. (A short attempt to run the specs on
Windows under cygwin failed miserably.)

This is a prerelease in code maturity (it's been only vetted by a couple of
people) and packaging: it is not yet available as a gem. Currently the code
can be accessed via git at git://github.com/dramatis/dramatis.git. 

The project web site is http://dramatis.mischance.net. This includes access
to the source code repository, issue tracker, rdoc documentation, and a
tutorial. Mailing list at http://groups.google.com/group/dramatis and IRC at
#dramatis on irc.freenode.net.

If you're daring and interested in actors and concurrency, have at.