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.
And, what surprised me more, it’s on steam. RetroArch is an emulator front-end - unified settings for many many emulators. The UI seems to be an acquired taste, but the documentation seems thorough.