Torque X is designed from the ground up to harness the power of XNA. Written entirely in C#, the result is an extremely powerful and flexible 2D & 3D game engine. You can code in C#, then run your game in Windows or on your own retail XBox 360 using XNA Game Studio 3.1 and XNA Creator's Club. Torque X is loaded with systems that make debugging, journaling game events and testing features much easier than with XNA Game Studio 3.1 alone. As of February 28 2011, Torque X will no longer be updated but will still be available for purchase from Garage Games.
This is the worst engine ever made by people claiming to be competent engineers. Stay away if you're at all serious about making a decent game.