Open licenced games and media.
I've played through most of the ones older than 7 years old.
Here are some solid start points:
Neverball, Kobo Deluxe, Project: Starfighter, Frozen Bubble, Hex-a-hop, SGT Puzzles, Numpty Physics, Fish Fillets NG, Enigma, Passage, Shattered Pixel Dungeon, X-Moto, Blobby Volley 2, Stormbaan Coureur, GCompris