Crysis 2 mod SDK, I am under the impresion that this is simply a modding tool.
Cryengine 3 SDK, I am not quite sure what this is for, but I want to know if I can place vehicles and watch them explode and such and admire the cryengine.
Sandbox, I have no clue as to what this is.
I am out of town right now and want to play around with the Cryengine, just goof off with the physics and such and admire the graphics. Crysis 1 or 2 is NOT installed on this computer.