X: Rebirth is set in the Albion space system which was established in X³: Albion Prelude. The player takes the role of Ren Utani who discovers the legendary space ship Albion Skunk and, together with his co-pilot Yisha, gets involved in the faction war between the governing Pultrach Mining Corporation and the Heart of Albion rebels. The campaign mostly serves as introduction to the game elements as the game's focus is still on player freedom.
X3: Terran Conflict is the latest appearance in the X-series by Egosoft. This is supposedly the final chapter. It's a space simulator, offering many possibilities to it's players, like fighting, trading, building factories, fleets, etc.
X3: Reunion is a space trading and combat simulator, sequel to the game X2: The Threat, and the third in the series.
X2: The Threat is a simulator based on Space trading and combat that is set in a fictional X-Universe. The game features over 50 different flyable ships, with a well told single player story.
