GOG Galaxy - Truly gamer friendly, DRM-free online gaming platform.
itch.io - An online game marketplace and community.
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.
Ubisoft Club - Ubisoft Club app enables you to get updates about your favorite games timely.
Playnite - Source code generated using layoutit.com