Torque Game Engine (TGE) from Garage Games - My team has extensively modified version 1.52. Now the fidelity of this engine is no where near the caliber of Unreal or Crytek, but it has 3 very distinct advantages. I recommend it to any indie developer, or student. The documentation however, has been a little lax, but is getting much much better. The ability to import models, a scripting language so you don't have to change the engine if you don't want too, and a large wiki of Q and A, this will get you going quickly.
- It is CHEAP in comparision. Many indie developers use this engine due to the price point. Under $250 when we purchased it for indie developer and $750 for commercial users (commercial is considered anything over $100K a year in sales).
- It comes with the source code for you to modify! Not many engines of this price (did I mention price?) come with the source code and allow for modifications at the base level. This is a boon if you need to add enterprise integration points like we did.
- Runs on multiple platforms - this particular version runs on Windows, Linux, and Mac with almost zero rework (there are two caveats, you have to code in independent libraries, and you have to have the different platforms on which to compile).
This is not to say there is not a downside to TGE. Sometimes the scripting makes you feel like you have entered the 7th ring of hell, but I find that with most modern computing languages. Anyway, if you questions about Torque, feel free to drop me a line (not that I am an expert, but I could point you in the right direction). Comments are most welcome (can I say PLEASE PLEASE?).
Have a great day!