Camelot's class system is based on Guilds. In much the same manner as Darkness Falls: The Crusade, players in Camelot start out as a base class, which is dependent on Realm, but usually includes Fighter, Acolyte, Rogue, and Mage. At 5th level all characters choose their career path by joining a guild. Their choice of guild determines what skills they get. Usually more than one base class can join each guild, resulting in several character types per guild. For example, an Albion Fighter can join the Guild of Shadows to become a Mercenary. A Rogue can join the same guild to become an Infiltrator.
Of course there will be player-created Associations as well, which will let same-realm characters band together and form their own organizations.