Aliens vs Predator 2 singleplayer custom map titled "RAS_Outpost_Defence_Survival".
Map author: Rasirez
This outpost map is somewhat of a tower defense and skirmish style map. The player spawns in a tower as the base is immediately overrun by aliens. There are turrets and guards located all over the base, but the aliens can easily gets past them most of the time. There is no real mission objective or ending to the map, but you'll probably want to get to high ground and get to the helicopter for safety. The map has somewhat of a Left 4 Dead feel with the rush to the helicopter.
The difficulty is fair, but you can be easily killed if swarmed. There are some bugs in the map such as rain coming through the ceiling and a filter over the whole screen that makes everything look a bit blurry at times. These bugs aren't too bad though. The map is very short but fun for a quick playthrough.