Regnum Online can be played over a few servers, which are distinct worlds. Servers offer the exact same content and gameplay, except for the experimental server. Once characters are created on a particular server, they cannot be moved to another (with a slight exception for the experimental server, see below).
NGD servers
There are two servers provided by the game development company NGD. They are operated, and their community is handled, by NGD, though the hardware itself is located in Sweden. Creating an account from the official website allows a player to create characters on both these servers, and the player can belong to a different realm on each server.
Ra (Spanish)
Ra is the the games oldest and main server, and is mainly populated by players from Argentina (where the developers are based) and other Spanish-speaking countries. However English-speaking players and clans do exist (see list from the official forum), and this server is where most veteran players play. The server is by far the most active, though this also has problems. Large battles between many players require a powerful computer for an acceptable frame rate, and ping times can go very high, particularly during invasions.
Horus (English)
Launched in August 2008, the Horus server was created to expand the game into the English-speaking world. English is the official main language of the server, though other language speaking clans exist. However the server is officially not available to Spanish-speaking countries; this restriction was created to give English the chance to develop as the server's primary language. Horus currently suffers slightly from low population: having only about 1/3rd the population of Ra, the war zone is not as active here, but this also means it suffers much less from lag problems. However the the server's population and activity are continuing to grow.
Horus is normally the recommended choice for new players outside the Spanish-speaking world.
Gamigo servers
These servers and their community are maintained by the German company Gamigo, and are only available to players with a Gamigo account. Patches for these servers are usually applied a couple of weeks after the international ones, in the case that there is content in need of translation to German.
There are three Gamigo servers. Two German ones named Niflheim and Muspell, and a French server named Nemon.These servers also have active GMs, something absent from the international servers. However there are more rules here, with strong enforcement, and the GMs are unpopular among some players.
Experimental server
The game has one public testing server, Amun. Its purpose is to test new features, fixes and overall polish. Upcoming patches will often be placed onto this server before being deployed to the main servers. The character database for this server is intermittently copied from the Ra server, and so the characters on this server can be erased without notice. The wipe frequency depends entirely on specific needs, sometimes it happens after a few months, sometimes it happens after a week.
The server has a few features to help in testing, there is a "global" chat channel for inter-realm communication, the /reset_powers command only takes 3 seconds instead of the usual 60, and there is an additional /train command that lets players modify their setup from anywhere, rather than just at a trainer.
However the availability of this server is not guaranteed, and sometimes it is only open to a select group of testers.
On this server, Ximerin gets decreased from a character's inventory but it doesn't get saved onto the database. Ximerin is only actually spent on the live servers. While Ximerin on this server doesn't get deducted from the players account, the minimum amount to buy the desired items is still required. This gives players an ability to test premium items before actually spending the Ximerin for real.
See also
Rankings: The war status, plus player and clan rankings, for each of the four gameplay servers.