Well, one of the alternatives is what ID Software used to do, where they would sell the game for a period of time and then open source the code Once sales dropped off.

Super Tux Kart is actually great. Open Arena is just Quake 3 with original art. IMO Open Arena is criminally underrated

The open sourcing of the quake engine is where a lot of modern engines got their roots.

Your posts always improve my day.