Retropie is a custom image of raspbian (the raspberry pi flavor of debian), so yes linux. It's really popular with the emulator crowd since it comes with about 20+ emulators and a front end based on emulation station. The one system it's missing that a lot of people want is colecovision.
I currently have a little box that does atari 2600, 5200, 7800, NES, SNES, DOOM I and II, Quake 3 and OpenArena. I *really* want coleco on this as well.
But yeah, it's ARM, not x86 so coolcv didn't run on the raspberry pi.