Oh~ this game looks like someone was really disappoined by how cube worlds dev killed the release on steam i guess. Thanks for that, i will check it out. tl;dr Game was gutted on steam release but so much more was already done, promised and/or teased.

InfraArcana was a little bit tough but is a very good roguelike

classicube is pretty cool, open source Minecraft classic-like game (so, no crafting or survival aspects, limited world sizes)

Only one that comes to mind is Lugaru. The creator had this weird legal battle where someone stole the game, ported it to iOS, and the thief claimed because it was open source he was allowed to sell it.

Aside from the other choices already mentioned (especially Doom stuff, FreeDoom ftw) any of the free games derived from the S.T.A.L.K.E.R. games and early builds, mostly Anomaly and Lost Alpha. There are also a few stabilized versions of the Build 1935 alpha out there which are worth playing and probably a bit more approachable for most people.

It's old but I always really liked WARSAW it was/is a quake3 port but with more cartoony outline graphics similar to Borderlands style.

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.

Pokemon Auto Chess. Literally what the name implies, a Pokemon auto battler 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.

Surprised it's not mentioned here, but Bzflag.

Super fun tank shooter game that doesn't take much to run, and reminds me of a cross between the very old bolo game and Mario kart's battle mode.

I'd say Pokemon Infinite Fusion. It's written in Rails and the artwork is done by the community

I've had a ton of fun in Red Eclipse over the years.

I made one! It's a solitaire-like but with some new mechanics, and fairly polished and balanced at this point. You can find it on itch and on the play store. Here's the source.

Cockatrice for playing TCGs / CCGs online.