Sven Co-op is, as the title suggests (the Co-op part, not the Sven part) a cooperative multiplayer game based on Valve's mega-hit FPS Half-Life. It actually began development as a Half-Life mod more than 15 years ago, but in the summer of 2013 Valve gave the team permission to release it as a standalone game on Steam. And today, it's finally happening

To celebrate the release, the developers are holding a 'release party on the Gamesurge IRC server—another testament to its aged roots. A guide detailing the capabilities of the new Angelscript plugins is also now available.

Sven Co-op was originally based on Half-Life and retains similar weapons, monsters, and characters, but the difficultly has been ramped up to support cooperative play. 'sven Co-op's levels are set as missions and are generally separate from each other. Many missions span several maps and some are collected together in a series," the game description states. "The aim of most levels is to reach the end or to achieve an objective—obtaining a high score is not essential to beat a level, it's just part of the fun.

And it looks like a ton of fun. Sven Co-op is available now—for free, by the way—on Steam.