Why would you think development of fluxus "has stopped"? The mailing list [1] is active enough for such a minority project, and the git repo [2] shows a reasonable activity for a mature (i.e. "done") project, with functionality commits from October last year, and French localisation commits from April this year (last one on the 19th, so less than 24h ago).
Excepting crashing bugs development depends a bit on when people have time or a need for a new feature but Fluxus is indeed still actively developed. As I see it it's indeed "done" in the sense of being useful for it's intended purpose right now, but there is space for big improvements like redoing the editor itself in Scheme, morefunctionality in the Windows version, etc. I'm personally working on and off on a little library for new ways of interacting with generative music in it. We're alive and well, I'd say.
Fair enough, but "OSX is not as well supported as I'd like" is a far cry from "has stopped development". FWIW, I get the updates just fine through Ubuntu PPAs.