It looks a lot like Dark Age of Camelot, and it is free to play,
Source: http://en.wikipedia.org/wiki/Regnum_Onlinewikipedia said:Overall Gameplay
The inspiration for Regnum Online is the online game Dark Age of Camelot (DAOC), specifically before DAOC introduced the capability to do crafting. As such, RO is heavily focussed on Realm vs Realm (also known as faction pvp or team pvp) combat. In general, at all times a player can find active wars occurring in the "Warzone" where players of the 3 realms fight for control of forts, gates and castles.