HalfLife.de has just posted a Sven Co-op interview, which includes some information on both Sven Co-op 3.0 for Half-Life/CS Retail and Sven Co-op for Half-Life 2.

Halflife.de: Hi Sven! Thanks for this interview. Just introduce yourself and tell us something about your Mod “Sven Co-op”?

Sven Viking: Hi Mathias!

I'm the SvenCo-op Team founder/team leader. SvenCo-op is a co-operative multiplayer mod for Half-Life, in which the players fight together against a horde of computer-controlled enemies. The mod also works with CS Retail (and possibly DoD Retail), though of course you will not have access to Half-Life's single-player storyline unless you own the original Half-Life.

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