I play a good deal of Simon Tatham's puzzles (iOS version) and Ordinary Puzzles (which is only one type.)

I've spent a good portion of the night trying to find some other open source / free / no IAP puzzle games, but for the most part I've come up empty.

Anybody know of some treasures out there?

I'd like to ask for recommendations for FLOSS (Free/Libre, Open-Source Software) games, playable on Linux or Android. I saw an old thread on this topic, but it's over a year old, so I thought it'd be okay to ask this year. Genre-wise, I'm pretty open. RPG, adventure, FPS, RTS, TBS, 4x, puzzle, sidescroller, platformer, single-player, multi-player, online, offline... whatever. I would prefer not needing to have original (commercial) game assets.

Fine print: I do like a good FPS, but, having played commercial titles on PS3 and PS4, I've found that the FLOSS FPSes I've tried just don't hold a candle to them. Also, I prefer having a short TTK (think: hardcore mode, R6S, BFV), and every FLOSS FPS I've tried has had a long TTK.

I've already played:

Linux:

• Wesnoth
• 0 A.D.
• roguelikes (currently have an active character in Angband)
• Ur Quan Masters
• Minetest
• bzflag (long ago)

Android:

• SuperTuxKart
• Pixel Dungeon
• Andor's Trail
• Mindustry
• Pixel Wheels
• Vector Pinball
• Minetest
• Wesnoth
• HyperRogue

What I haven't played, but might check out:

• FreeOrion
• Endless Sky
• Glest, MegaGlest
• Warzone 2100
• Zero-K
• KeeperRL
• OpenRCT2
• Oolite