On the Windows side of things they rely on DirectX for PS2 and Gamecube emulation and it leaves me wondering how quickly they'll write a suitable OS X analog for it.
PS1 and N64 support will be coming soon along with other platforms. You will have to provide your own BIOS though. It will be cool to have those, especially with the PS emulator and games all in one app.
PS2 will be cool to see since all the emulators I've tried never worked so good. ePSXe has been great so far though. I love how easily the PS3 Six Axis works too. OpenEMU has done a tremendous job on this so far.
I have installed the experimental build of OpenEmu with allows you to download the MAME core to play Arcade ROMs but nothing happens when I try to open any of them. I understand this feature is in beta but have heard others have been to play various ROMs. Any suggestions to resolve is greatly appreciated, thanks!