Portal 2 is a first-person puzzle game. It consists of a number of puzzles to be solved by teleporting oneself to other planes. It has nice 3D effects.
Portal 2 Coop is a launcher that supports search, custom maps, hosting and connecting, nickname, etc. Portal 2 is actually a single player game. With this program, we can connect to other players online.
You can get custom maps from www.thinkingwithportals.com.