exeem's creators have said a linux version is planned once the windows version reaches 1.0... they didn't make any commitment whatsoever to a Mac version, but the faq on their page sounds like they might consider it if there's enough interest.
Anyway, exeem is not open source. Any O.S. implementation would have to be reverse-engineered, and I don't think the protocol is stable enough at this point to even begin contemplating such a project.
Nope, exeem is stuck on Windows for awhile.