Series of space combat games developed by Egosoft. X - Beyond the Frontier was released in 1999, and was followed by the X-Tensions expansion. X2 was due to be released in 2002. X2OL, or Online-Universe, is a massively-multiplayer sequel to X2. The games involve a mixture of fighter combat and trading.
This category does not list sites related to the X-COM games.
Expansion based on X - Beyond the Frontier, released in 2000. X-Tension added greater freedom of gameplay to the first title, and expanded certain features, such as ships available. X-Tension was also bundled with X - Beyond the Frontier under the name X-Gold.