The Matrix Online (also known as Matrix Online) was a massively multiplayer online game developed by Monolith Productions created by Richard Carroll. It was the official continuation of the storyline of the Matrix series of films. The game began closed beta-testing in June 2004 which was then opened for people who pre-ordered the game in November 2004. Warner Bros. and Sega officially released MxO on March 22, 2005 in the United States. It was released in Europe on April 15, 2005. The game ran continuously from then until it was ultimately shut down on July 31, 2009 by Sony Online Entertainment.
The player assumes the role of a redpill, a human who was formerly trapped inside the Matrix. When creating a new character, the player is given the choice of taking a blue pill that will return them to their former life (quit the game) or a red pill, which will free their minds from the Matrix. Characters who are unaware of the fact that they are in the simulation are often referred to as "bluepills" because they have either taken the blue pill or have not been given the choice yet. People who are aware of the simulation (players) are referred to as "redpills" because they have taken the red pill (or, in very rare cases, when a character has self-substantiated out of the Matrix on their own). Following the choice between the two pills, the player is then taken through a basic tutorial of the game's mechanics, including mission interaction and the combat system. After the tutorial, they are then free to roam the Mega City (the large metropolis that the entire Matrix story is set in).
Source: Wikipedia, "The Matrix Online," available under the CC-BY-SA License.