XMonad is supposed to have OS X support but I've heard it only works for X11 apps. It'd be great to have XMonad for OS X fully supported because once you get a good config built up it's hard to beat. And if you know Haskell it's even better.

You can totally write XMonad as a Hydra config or extension. Honestly I expect someone to do it any day now, considering how fun it sounds.

If anyone tackles this, please submit it to https://github.com/sdegutis/hydra-ext

EDIT: I forgot that this would require the events feature, which is planned for the 1.1 release. So not all of XMonad is possible in Hydra yet, although most of it is.

This issue[0] was what was keeping xmonad from building for me, though I don't have a mac to try on again.

0: https://github.com/haskell-pkg-janitors/X11/issues/24