From video gaming to card games and stuff in between, if it's gaming you can probably discuss it here!
See also Gaming's sister community Tabletop Gaming.
This community's icon was made by Aaron Schneider, under the CC-BY-NC-SA 4.0 license.
I'm surprised to not see Flare RPG mentioned. It's nothing groundbreaking on its own, but it's actually got two nicely fleshed out campaigns, and tooling for people to make new ones. It's a nice, fun, FOSS single-player RPG, and it's great if you want that old fashioned Diablo feel.
Another vote for Endless Sky here as well, it's just excellent, and surprisingly expansive.
I've had a ton of fun in Red Eclipse over the years.
InfraArcana was a little bit tough but is a very good roguelike
How does it compare to something like Brogue?
I haven't played Brogue but in nutshell IA is a proper roguelike and somehow manages to create the atmosphere of being alone in the dark in a mansion full of acolytes and worse
Pokemon Auto Chess. Literally what the name implies, a Pokemon auto battler fan game. Honestly it's really well-polished for something only a couple of people are working on (aside from commissioned sprite artists) and has an active community to go with it.
Terminal games:
Adventure - A classic adventure game. (In the BSDGames package) Hack - The game that inspired NetHack. (In the BSDGames package) Greed - A game where you go through a number field, eating the numbers. It's hard to explain but very fun. Rouge - It's nice to go back to the classics. I like Hack a bit more though.
Non-Terminal Games:
Secret Maryo Chronicles - It's like Super Mario Bros. Alien Arena - Kind of like natural selection. Urban Terror - Kind of like Counter-Strike Warsow - Kind of like Quake. Xonotic - Like Quake again.
I think that's all I played back in the day.
Warzone 2100. It reminds me of the older Command & Conquer games with a ton of upgrades and customization for your units.
Technically not the whole game, but Smash Remix is an open source rom hack of the original Super Smash Bros. for the Nintendo 64. It's been a blast from the past and I'm enjoying the hell out of it.
I also love the fact that a lot of N64 emulators are open source too, like Mupen64 or simple64
The only one Ive played for any length of time is freeciv, which as the name implies is based of the civilization games, mostly civ2. It's a bit old looking these days and setting up multiplayer has always been a bit fiddly, but the gameplay is pretty fun imo.
I always used to love playing Freeciv years ago as I grew up on Civ 2 and Civilisation: Call to Power. Probably should try it out again on a modern OS.