It's not often you see such a complete package for Raspberry Pi. Recalbox is an all-in-one OS with a target audience of retro gaming enthusiasts. It includes emulators for over 40 systems (for example NES, SNES, MAME, Playstation, Megadrive), an easy-to-use UI using EmulationStation, support for multiple gamepads (PS3, Xbox360, even a smartphone touchscreen!), and last but not least, a full media center support with installed Kodi onboard.
As an additional bonus a web interface is available for the OS, so you can for example manage all your installed games and start them up remotely via the web browser.