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.
A new version of Team Fortress 3! What add update read in description
Why is this in Addons as the "Multiplayer Map", rather its own mod page?
Well actually, inside of this mod I found contents for Half-Life 2 and Half-Life 2 Deathmatch labeled as "hl2" and "hl2mp", which bloat the package size.