I'm in the progress of updating Nuketown's Mac Role-Playing Game Tools page, which has developed an embarassing case of bitrot.
Unfortunately some of the more stalwart tools, like Crystal Ball, as well as one-offs like the Town Creator and D&D Manager, are no longer available, and their sites have gone to the Great Bit Bucket in the Sky. Still others, like Dunjinni, no longer work with under Mac OS Lion and don't seem likely to be updated any time soon.
As such, there's aren't a whole lot of tools featured on the page that are actually still working. And yet, I know from researching my "Summon Web Scryer" columns for Knights of the Dinner Table that Mac compatible tools do still exist. Many of these are Java based apps that are platform indepenent, which may make them even more appealing to gamers who want to share their creations with other players.
Know of a Mac-centric app that deserves promotion? Post it as a comment below, and I'll add it to the features page as I rebuild it.