Honestly, I never stop being amazed at how little press this game gets, especially when given the backstory.
The Dark Mod is a free game that emulates Thief 1/2 gameplay in a heavily-modified Doom 3 engine. It has a level editor and is actively updated with an online community.
If you ever wanted to see what a real Thief 3 would've been like, this is the closest that you'll ever get. Everyone should at least download and play it once in their life.
Can I still play Super Turbo Turkey Puncher?