Mac version?

As far as I know, there isn't one and I haven't heard of plans to make a Mac build. Myself, being a person who dislikes Apple and everything to do with them, am fine with this. I think you could try Mupen64, though, that one's cross-platform, and not a bad emulator at all.

Mupen64 - Wikipedia, the free encyclopedia
Mupen64 web site (downloads page)

Better yet, try out Sixtyforce! Works real well with a bunch of games.

Trust me and everyone else: they will NEVER make Project64 for Mac.

You'll need to use Sixtyforce or join in on the Mupen64Plus crowd to see when a Mac version will be available.