1 - X-COM: UFO Defense
Released on Mar 01st 1994
2 - X-COM: Apocalypse
Platforms:
PC (Microsoft Windows), DOS
Released on Jun 30th 1997
3 - Magic & Mayhem
Platform:
PC (Microsoft Windows)
Released on Dec 07th 1998
4 - Lords of Chaos
Released on Dec 31st 1990