RetroArch - RetroArch is a frontend for emulators, game engines and media players.
The Indie Gala - Buy a bundle of games, you decide the price, and support charity in the process.
Batocera.linux - Batocera.linux is an open-source and completely free retro-gaming distribution that can be copied to a USB stick or an SD card with the aim of turning any computer/nano computer into a gaming console during a game or permanently.
Fanatical - Buy awesome games. Pay a fraction of the retail price!
Playnite - Source code generated using layoutit.com
Humble Bundle - Buy a bundle of games, you decide the price, and support charity in the process.