Hello, and welcome to "Games, but with friends" or simply: Gabuwif.

In case you ever get bored of steam games, and you're looking for some new things to play, I have a list; and some short descriptions.

Golden Age Of Civilisations: https://www.gacivs.info/
It's a Civ-esque game with some extra time elements added.

OpenSpades: http://openspades.yvt.jp/
A clone of a very early version of Ace Of Spades, a cool block-based shooter with an active community, and has emergent tactics, such as pillboxes and trenches, as well as other things.

OpenClonk: http://www.openclonk.org/
Strange but fun game, sort of a mix between Worms, Minecraft, and Civilisation. The game has several modes in both singleplayer and multiplayer, and involves mechanics such as mining, settlement and full-on wars.

Speed Dreams: http://www.speed-dreams.org/
A motorsport sim, with an active community that mods the game, as well as such antique features like Split Screen. Quite a fun game to play.

Xonotic: http://xonotic.org/
A visually impressive and well-optimised FPS, as well as fast paced. It plays a wee bit like Quake.
I am unsure about community, but if you like it, post a discussion to see if we should play.

Globulation 2: https://globulation2.org
A top-down RTS, that attempts (well, I add) to cut down on micromanagement as much as possible by automatically setting tasks to worker units, with some customisations. I couldn't get too much info on this one, sorry guys.

Rigs Of Rods: http://rigsofrods.org/
This game started out as a truck racing game, eventually evolved into a crazy sandbox game, in similar vein to BeamNG Drive, with planes and props and boats, it's fun if you're into it. Oh, and it has up to 64 players in multiplayer. How sick is that?

Oolite: http://oolite.org/
If you enjoy Elite-like games, with complicated yet rewarding gameplay and dubious ship controls, this is for you. It'll suck you in, as soon as you get a handle of the controls.

Lugaru HD: https://osslugaru.gitlab.io/
Now, what would an Open Source Games list be without Lugaru? Fast paced, difficult, but amazingly satisfying bunny-fisting action. What more could you want? It also comes with multiple story based campaigns.

The Battle For Wesnoth: http://www.wesnoth.org/
A TBS with multiple varied races, and quite fast-paced gaming, a fun and challenging game with a good modding community.

WorldForge: https://www.worldforge.org/
Cool tool for creating MMORPG's, personally do not know much about it. You can also join other people's MMORPG's.

And, finally, a free flight sim called:
Flight Gear: http://www.flightgear.org/
A free flight sim. Similar to Microsoft Flight sim, only free.

That's the end of my list. Tell me if you know any more games.