PMABlades has posted up at PlayMyth what FlyingFlip Studios been up to lately (besides playing Fable):

The most noteworthy of these things is a Linux port of the Myth III world editor Ballistic. During the last few months we've been making several updates to Ballistic and work continues in that regard, but a few of the more curious amongst us thought it might be cool to try to get things working in a Linux environment.

There is also a thread with screenshots. Of course, Myth editing on Linux without Myth playing on Linux is a bit silly... but it sounds like something may be in the works on that front as well, as far as Myth 3 is concerned.