Cloned Cube is a Portal mod. It takes place after GLaDOS' fall in Portal. You assume the role of Chell's secret clone. You have to escape or else you may just be tested to death. There is one obstacle. CUBiS is trying to kill you.
Images from the Alpha version of level 1. Currently you escape, grab the Portal Gun, escape a turret, find a rocket turret, and solve the puzzle to press the button to open the secret elevator.