UPDATE:There is a new version of the game, visit the official site.
THE DARK MOD 2.0 is a free, first-person stealth game inspired by the Thief series by Looking Glass Studios. It recreates the essence of the original Thief games on a more modern engine. Both a game and a mission-creation platform, The Dark Mod allows players and mappers alike to enjoy missions in a gothic steampunk universe.
The Dark Mod was officially released on October 17th, 2009. As of October, 2013, TDM 2.0 is now completely standalone, and no longer requires Doom3.
8BitMMO is a retro-style 2D massively multiplayer game! It’s a giant construction sandbox — you can build a home or a castle in a persistent streaming world. Found and manage your own city. Fight evil Lawyercats and engage in player vs player battle. Work in Progress!
Cube Trains is a free puzzle game where you build elevated railways in a city. It features 3D puzzles, unlimited undo/redo, and smart placement of pieces. The non-linear level graph means you don’t have to beat a level before unlocking the next one. The game comes with a built-in level editor, so you can build and share your own corners of the city.
Savage XR is the successor of the 2003 award winning PC game “Savage: Battle for Newerth”, delivers unique team-based gameplay, Real Time Strategy Shooter (RTSS) genre. For Windows (XP/Vista/7/8), Linux (Ubuntu/Mint/Debian/Fedora) and Mac (Intel Macs only).
Topdown tactical RPG roguelike game and game engine. Tales of Maj’Eyal (ToME) is a free, open source roguelike RPG, featuring tactical turn-based combat and advanced character building. Play as one of many unique races and classes in the lore-filled world of Eyal, exploring random dungeons, facing challenging battles, and developing characters with your own tailored mix of abilities and powers.
Open Mortal is a parody of the once popular coin-up fighting game, Mortal Kombat, for Windows and Linux. It is currently playable, has 18 playable characters. There is network game, team mode, etc. You can even add your own character.