- X: Beyond the Frontier
- X: Tension
- X2: The Threat
- X3: Reunion
- X3: Terran Conflict
- X4: Foundations
- Xargon
- X-COM: Apocalypse
- X-COM: Chimera Squad
- X-COM: Terror from the Deep
- X-COM: UFO Defense (UFO: Enemy Unknown)
- X-COM 2
- X-COM 2: War of the Chosen
- Xenon
- Xenon 2: Megablast
- Xixit