To be honest: I'd subscribe to the
free games thread. The humble store and (especially) epic give away very decent games on a regular basis. You only need to click a bit and have a launcher and account ready to be good to go. Once claimed, it remains yours (or more specifically: the account's) forever.
Epic had GTA5 just last week, and are now giving out civilisation 6, so...certainly no bad stuff.
As for genuinely free games...most modern ones have been mentioned, so I'll dive into some older abandonware:
-Lost vikings (early blizzard platforming game about controlling 3 characters)
-the incredible machine series (complete the contraptions)
-transport tycoon deluxe (and/or openTTD)
...and I'm not sure if I'm allowed to link to the site, but it seems like Simpsons hit & run, black & white and even rayman origins are now abandonware, and thus (legally?) free to download and play.
