RetroArch - RetroArch is a frontend for emulators, game engines and media players.
GOG.com - DRM-free game store, selling both new and old titles. No clients required.
Lutris - Lutris is an open source gaming platform for GNU/Linux.
Origin - Origin is your new digital playground. It’s where you go to find the best that EA has to offer.
mGBA - mGBA is an open source emulator of the Game Boy Advance. The goals are speed and accuracy.
Epic Games - Computer game storefront that gives 88% of revenue to developers