Although personally I am more of a B1 In Search of the Unknown person, B2 The Keep on the Borderlands apparently resonated with a huge audience, as it continues to inspire homages almost 40 years later. The most recent homage is the first product from John Leeper and Grey Goblin Games, FP1 Arrival At Fort Perilous. The modestly priced ($2.20) 30 page module follows that basic setup, almost exactly, there is a lone (more or less) outpost in the wilderness that serves as a home base for low level parties to go out and explore.
The difference is, rather than one large, multi-faction dungeon to explore, there are three separate smaller dungeons, two out in the wilderness, one essentially part of the fort itself (well, right outside), each with a single faction.
