[Duion]

What would be the use of that? Are you trying to build a pseudo 2D game with like a top down view, but 3D graphics? If that is the case, you can just leave everything 3D and just lock the camera.

[Jozor]

Torque2d supports doing this as you can have 3d models and animations in it.

[JeffR]

Also, you could just do a simple bounds or capsule collision on a 3d object in T3D. Anything moving around would collide with that and be blocked as well.