Game launchers

Steam

The most popular way to play games on Ubuntu is Steam.

GOG

Minigalaxy is a simple GOG client for Linux.

Read more on the Minigalaxy GitHub page.

Also available as a flatpak.

Alternative launchers

Some games, such as those purchased on Humble Bundle, do not have a dedicated launcher on Ubuntu yet. Alternative launchers are available for these and other games.

Two of the most popular alternative launchers, both available as flatpaks, are:

Lutris: the Lutris Flatpak seems to be up to date with releases in the official Lutris repo.
Heroic launcher: the Heroic Flatpak is recommend. An AppImage is also available.