Sven Co-op is a co-operative game originally based around Valve Software's Half-Life. In this game players must work together against computer controlled enemies and solve puzzles as a team. Sven Co-op uses the GoldSrc game engine. The modification enables a server to many players to cooperate among themselves and allied non-player characters in completing levels against creatures and other enemies that are controlled by the computer. The modification was initially based around the levels from Half-Life, but since have expanded to include the other Half-Life games and user-made levels. Multiple levels may be put together to make a longer campaign by the level designer. The game can also be played in single player mode, taking advances of improvements over the original Half-Life that were made by the modifications, particularly for the artificial intelligence used by non-player characters.