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.
The alpha 0.1 version of Cloned Cube. Requires 7-zip. Extract to your Sourcemods directory in Steam, restart steam, and press on the Cloned Cube item in your game list.