Best and most in-depth mmorpgs rely on player with player interaction. Having an environment where players may freely attack themselves and combining it with the death penalty element (item loss) is what makes countless possibilities for interaction available...

Free for all PvP was first introduced for developing purposes in the 'mangos' community.
The mechanism behind it is simple - it marks all the map as an open world arena so anyone may attack anyone, anywhere.

This is an ambitious move aiming to deliver the ultimate player vs. player experience and also allow for co-operative parties or guilds to be created in protection or in war with the players at a certain area and whatever else you could possibly imagine in an open world free for all pvp environment. Enjoy!