The Left 4 Dead branch is an overhaul of many aspects of the Source engine through the development of the "Left 4 Dead" series. Multiprocessor support was further expanded, allowing for features like split screen multiplayer, additional post-processing effects, event scripting with Squirrel, and the highly-dynamic AI Director. The menu interface was re-implemented with a new layout designed to be more console-oriented. This branch later fueled the releases of "Alien Swarm" and "Portal 2", the former released with source code outlining many of the changes made since the branch began. "Portal 2", in addition, served as the result of Valve taking the problem of porting to PlayStation 3 in-house, and in combination with Steamworks integration creating what they called "the best console version of the game".