This app is absolutely amazing, and never did I think one program could house so many emulators in one package. Because of this app, I was finally able to play TG-16/PC-E/CD, Sega Saturn, and several other things from where I couldn't before on my previous Macbook. Hands down, this application is fantastic. The only quirk it could use is fixing the framerate on certain cores for the emulators provided, they can be somewhat jerky in some spots.
I wish though, in the future, that it could possibly hold in a Sharp X68000 emulator because there are indeed emulators for that system and I don't see any reason why OpenEmu never opened up to that particular one. There are some fantastic games on that system and it'd be a shame if it never saw the light of day on that application (I definitely want to try Cho Ren Sha 68K badly since the Windows version can only work so far to a degree with Wine, and it isn't perfect).
If you own a Mac with either Mavericks or Yosemite installed, you have no reason not to have that app on your computer. It's definitely worth it.
...I do wish that there was a forum somewhere for OpenEmu devs, but all they have is a GitHub. :T