I got it for free from that game store everyone hates for all the right reasons.

A gaming sub free from the hype and oversaturation of current releases, catering to gamers who wait at least 12 months after release to play a game. Whether it’s price, waiting for bugs/issues to be patched, DLC to be released, don’t meet the system requirements, or just haven’t had the time to keep up with the latest releases.
No memes please.
Is this gameimage tool some kind of archiver/packer? Seems interesting
Indeed it creates an flatimage, a file containing a base linux install and a runner of your choice. Wine staging for instance (Emulators also). You can add programs and or games to the package. Creating a one click solution to run software/game(s) without the need of aditional configuration afterwards like with lutris.
Works on all distros
For more info have a look over here: https://github.com/ruanformigoni/gameimage