Here's one I've not heard of before! Quetoo (originally Quake2World), a free and open source FPS that's currently in Beta is asking for votes on Steam Greenlight.
'Action Half-Life 2' version 3, a source-based modification aimed at simulating the experience of being in an action movie has released and it now has Linux support.
Shortly after reaching the milestone of one million downloads on December 12th, 2016, the single developer of Ravenfield announced that a paid version of the game is being prepared, and right now a Steam Greenlight page is already up.
This is a small adventure that has been out there for two years, but since it never was covered in GOL, I decided to try it and share with you some impressions. Also, you can't miss the funny DLC included.
X-COM: UFO Defense is a true classic. I played it originally on Amiga for days on end and it has a fully functional open source engine from the community named 'OpenXcom'. The game is free right now on Humble Store, so go grab it.
Streets of Rogue, the rather excellent open-world roguelike has been updated again. Two major new features for the online mode are NAT punch-through and automatic port forwarding to make connections easier.
Angeldust is a late night discovery after trawling through Steam around midnight last night. It's free to play, looks amusing with the colourful cartoon-like characters so I gave it a go.
If you're looking to play an adventure game but you don't have a lot of time, then you may be interested to check "Sisyphus Reborn", a lightweight (300 MB) and short existential adventure that will only take you 40 minutes to finish (and that includes getting all the achievements).
0 A.D. Alpha 21 Ulysses is the latest and greatest open source real time strategy game, and probably one of the most high quality open source games around.
Streets of Rogue is already an extremely cool game, but now it's about to get even cooler. The developer mentioned to a GOL follower than he is planning online co-op support!
Disturbed is a visual adventure with hand-made black and white graphics, where you play as a farmer who needs to save his land from a horrific plague before it's too late. It's FREE.