ClockworkOS ships with retroarch installed, with folders and configurations pre-created for:
- MAME
- GBA (MGBA)
- NES (NESTOPIA)
- PS1 (PCSX)
But since RetroArch is included, Adding support for other emulators is a breeze with cores, on mine I added SNES, and GB (With options for others, but those are the ones I wanted). Refer to this article for information on adding other emulator support: RetroArch Megathread or even this How to add new emulators (Gameboy, SNES, etc.)
With v0.21 (just released), they also added:
( * Not really retro emulators )
Hope this helps! GameShell runs atop a linux enviroment. So with some quick learning of SSH access, you can do a lot with this little thing!