I'm looking for a server side tower defense type mod. Basically something where after X days you get bombarded with bad guys. and you have to build yourself a base before they all come after you and try to survive. Anything like that exist?
No there isnt. Even if someone would try it would take months(Not serious speaking), though it would be kind of impossible since bukkit isnt finished yet so i dont think thoose features are released yet.
There are several plugins out there which allow you to spawn NPCs en masse. I think I can even remember seeing one which let's you direct them at some point/player.