Unciv if you enjoy sacrificing hours of your life :)

Cataclysm: Dark Days Ahead, or if you like something a little less complex, Cataclysm: Bright Nights, are fantastic roguelike games. Proper traditional, turn based, tileset ones.

Imagine a mix of Fallout and The Walking Dead, that's what it's like. It's superb. The possibilities are endless

Veloren is based on Cube World and it's an RPG with server builds and everything

Great suggestions in this discussion! Rather than adding my favourites, I will add some resources that list more games.

• Libregamewiki: it is really comprehensive (sometimes too much, including even not-so-good-games). They care about licencing and is is very easy to browse, top-notch for me.
• Open source games: a more relaxed repository, with lots of material.
• bobeff open source list: this is curated, which means that there are not so many games but each and every one is stable, good, maintained.
• Arcane Cache: a fantastic blog with reviews of libre games — or more precisely, underground games, there is a lot of discussion on how gamedevving philosophy too. The reviews are always in-depth and allow you to experience the games on another level, and each game is a small jewel in its category. Strongly recommended!

I liked oolite and doomrl .

Shattered Pixel Dungeon Roguelike, very addctive :)

Havent seen endless sky mentioned here, it is an old school space trader sim (think scape velocity or a 2d freelancer)

Ive been playing a lot of MineClone2 which is a modpack for Minetest!

Battle for westnoth !

And I can't remember right now the stealth game I used to play, it was the dark something, gonna search it later.

I like re3, reVC and reLCS. These are reverse engineered versions of GTA 3, Vice City and Liberty City Stories with improvements. Take Two has thrown a strike on the main repository, but you can still find mirrors or builds in the internet.

I used to play Sauerbraten, a Quake-like FPS, way back in the day. Doesn't look like it's very active any more.

A lot of good tips here, but you should have a look at Endless Sky! Really cool space game
https://github.com/endless-sky/endless-sky

Amnesia: The Dark Descent and Amnesia: A Machine for Pigs got open sourced if that counts.

• Xonotic is a great old school, Quake style FPS with an active community
• 0 A.D. is a pretty polished historical RTS
• The Battle for Wesnoth is a classic turn based strategy
• OpenRA is an open implementation of the Red Alert engine that's got an active community
• Openhv is an OpenRA based sci-fi RTS

NetHack - Roguelike

Space Cadet Pinball - Decompilation of 3D Pinball for Windows – Space Cadet

The Battle for Wesnoth - Turn-based strategy game with a high fantasy theme

Mindustry - Sandbox tower-defense game

Minetest - Voxel game engine