Full Invasion 2 is a co-op module for Mount & Blade: Warband where players come together to survive countless waves of invading enemies and bosses. It has been voted one of the most popular multiplayer modules within the community, and is still under active development to this day.
Probably the best mod for Warband and the only one I played for over a month. It has some small problems, mostly personal for me, but other than that its just beautiful.