Sven Co-op

The Steam version of Sven Co-op is a Valve-approved standalone version of a mod for Half-Life which allows cooperative play in all of its missions, which it comes bundled with for free. In addition, it includes Half-Life: Uplink that is also modified for this game mode, as well as some community-made co-op maps. In the game directory, there are also batch scripts which allow the player to import Opposing Force and Blue Shift missions if they are found installed on the system. A special hub level can also be used to travel between Half-Life and expansion chapters.

Aside from the mission content, Sven Co-op has its own set of player and weapon models, some of which are replacements/improvements for existing ones and some being entirely new (e.g. various soldier skins, female Black Mesa guards Barniel and Kate, and more), an SDK and a dedicated server application. The game runs on a heavily edited GoldSrc engine, labeled "Svengine", which allows for some unique functions and fixes.