Factions is a PvP-based plugin for MineCraft. I personally don't think it's a very good one, because it adds too much protection. You can claim land using power that you get by having players in your faction, and it's protected from other players. Also, you take less damage in your own faction's territory. You lose power when faction members die, and if your power is less than your land, other people can start claiming you land. However, this is really exploitable by just making an obsidian wall around your base, or covering it in water, then you're invincible to TNT cannons, which is pretty lame. Anarchy with a party system to disable "friendly-fire" is a lot more fun IMO.