GlouOSGame launchers
Beyond Steam, GlouOS makes it easy to play games from every other store too.
Lutris
Lutris is an open gaming platform that installs and manages games from many sources with community-made setup scripts.
Heroic (Epic & GOG)
Heroic is a launcher for your Epic Games Store and GOG libraries, with cloud saves and per-game settings.
Bottles
Bottles runs Windows software in isolated environments, handy for launchers or tools that do not have a native version.