"Half-Life: Blue Shift Coop" allows you to play Blue Shift cooperative. It's not recommended to people that hate bugs, since running Blue Shift cooperative is very buggy due Blue Shift was not meant as an online game. Also, Blue Shift uses another bsp format then Half-Life, so nothing in the maps are changed at all. You must have Blue Shift on Steam in order to play Blue Shift Coop, it won't work on Won due to invalid cd key error message. You must also either have an LAN or internet connection.