It's taken 17 years, but the Sven Co-op mod, a co-operative game based on Half-Life, will be released as a standalone title on Steam this coming Friday.
The game started as a fan project back in 1999 two months after the release of Half-Life. The first public version of the Sven Co-op mod was uploaded to the Atomic Half-Life fan site.
Since then, Valve the team with a Goldsrc license which allowed them to update the engine to "surpass the limitations of standard mods."
In it, players will need to work together against computer controlled enemies and solve puzzles.
Weapons, monsters and characters in the game are similar to Half-Life and the difficulty "has been increased to suit team play."
Levels are set as missions and some span several maps with the goal to reach the end or to achieve an objective.
Sven Co-op will be available to download for free on January 22. According to the developer, all donors past and present will be able to keep the bonus features in the Steam version.
The Steam release will also contain frequent iterative updates and Steam Workshop support at some point.
You can find out more on the Half-Life co-op mod through the official website.