Pick up the crowbar of research scientist Gordon Freeman, who finds himself on an alien-infested Earth being picked to the bone, its resources depleted, its populace dwindling. Freeman is thrust into the unenviable role of rescuing the world from the wrong he unleashed back at Black Mesa. And a lot of people, people he cares about, are counting on him.
Source Engine Co-Operative Base Modification (Seco7 for short) is a modification designed solely for Half Life 2 MP SDK Modification Teams to add additional features quickly and easily into their newly created Source Engine 2007 Half-Life 2 Multiplayer modifications. While no true support is given, if you do run into problems the best place for answers is the steam coding forums. It adds support for such features as AI, Multiplayer Vehicle Support, Player Classes (with custom class attributes), Dynamic Valve Game Mounting (including Portal content), Level Transitions with Save and Restore Functionality and much, much more. The archive also contains a compiled modification, allowing you to see for yourself the co-operative base in action. Though of course, you'll do so much better and more with it than the example maps given.