Mitch - The unofficial mobile app for itch.io
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
GameDatum.com - A platfrom of free online games. A list of all the available online free games from various producers online.
Playnite - Source code generated using layoutit.com
ScienceGameCenter - The goal of the Science Game Center is to demonstrate to teachers, scientists, museums, and parents the myriad ways games can be used to improve education in math and science.
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.