Batocera.linux: Batocera.linux is an operating system (like Windows 10 and Mac OS) specialized in retrogaming available for your pc and different nano computers like the Raspberry and the Odroids
On PC, it is available on a usb key and can boot without altering your existing hard drive. Note that you must own games you play in order to respect legality.
Lakka: Lakka is a lightweight Linux distribution that transforms a small computer into a full blown retrogaming console.
Recalbox: Recalbox allows you to re-play a variety of videogame consoles and platforms in your living room, with ease! Recalbox OS is free, open source and designed to let you create your very own Recalbox in no time! Use Raspberry Pi, ODROID or even PC (x86)!
RetroArch: RetroArch is a frontend for emulators, game engines and media players. It enables you to run classic games on a wide range of computers and consoles through its slick graphical interface. Settings are also unified so configuration is done once and for all.
RetroPie: Welcome to RetroPie. RetroPie allows you to turn your Raspberry Pi, ODroid C1/C2, or PC into a retro-gaming machine. It builds upon Raspbian, EmulationStation, RetroArch and many other projects to enable you to play your favourite Arcade, home-console, and classic PC games with the minimum set-up. For power users it also provides a large variety of configuration tools to customise the system as you want. RetroPie sits on top of a full OS, you can install it on an existing Raspbian, or start with the RetroPie image and add additional software later. It's up to you.