From Wikipedia: "Achaea is operated by collecting the revenue through a microtransaction system, which allows payment for the acquisition of in-game benefits. In the game, players explore a fantasy sword and sorcery world revolving around six city-states and their respective Houses. As in most role-playing games, players can fight monsters for experience points and treasure, perform quests for non-player characters and interact with other players. One of the major forms of interaction is player vs. player combat, where the dynamic conflict, especially the conflict between Good and Evil plays a dominant role in Achaea. The other play mechanics include the free market economics, which allows the players to design and craft goods, and the player-run social structure, including Houses (formerly guilds) and politics.... More Info »
The world consists of over twenty thousand locations, known as rooms, ranging from common countryside to more exotic and surreal environments. Players may choose among eighteen classes, ranging from familiar fantasy elements such as paladins to more unusual options such as Tarot-using Occultists.
Recent structural changes have enriched the environment of Achaea further, by opening up the seas to player controlled ships. This has made available many minigames including diving for treasure, deep-sea fishing and even a form of piracy.
Achaea's controversial revenue structure has received attention from the game development industry. Although Iron Realms Entertainment provides a custom MUD interface for the game, there are neither up-front costs, nor monthly fees typical for the MMORPG-genre. Instead, players may spend money for credits that are then used in-game to acquire skills and superior equipment.
Recently, however, Achaea has somewhat deviated from this model. In early 2010, the option to purchase an Iron Elite membership became available, which periodically gives players credits and other bonuses in exchange for a monthly fee.