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 (idTech4 aka the Doom3 engine, but modernized after it went open-source). 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 as a base.
The source-code is available under the GPLv3 or later, while the art assets are freely modifiable albeit only for non commercial purposes (CC-by-NC-SA 3.0).