UFO/X-COM

(1981) Aftermath! (unrelated post-apocalyptic role-playing game)
(1984) Rebelstar Raiders (Julian Gollop/Red Shift)
(1985) Chaos: The Battle of Wizards (Julian Gollop/Games Workshop)
(1986) Rebelstar (Julian Gollop/Firebird)
(1988) Rebelstar II (Julian Gollop/Silverbird Software)
(1988) Laser Squad (Mythos Games/Blade Software/MicroLeague)
(1990) Lords of Chaos (Mythos Games/Blade Software)
(1994) UFO: Enemy Unknown/X-COM: UFO Defense (Mythos Games/MicroProse)
(1995) X-COM: Terror from the Deep (MicroProse)
(1997) X-COM: Apocalypse (Mythos Games/Blade Software)
(1998) Magic & Mayhem (Mythos Games/Virgin Interactive/Bethesda)
(2001) Original War (ALTAR/Virgin Interactive)
(2002) Laser Squad Nemesis (Julian Gollop/Codo Technologies)
(2003) UFO: Aftermath (ALTAR/Virgin Interactive) (The Dreamland Chronicles: Freedom Ridge)(2005) Rebelstar: Tactical Command (Julian Gollop/Codo Technologies/Namco)
(2005) UFO: Aftershock (ALTAR/1С)
(2007) UFO: Afterlight (ALTAR/TopWare)
(2012) XCOM: Enemy Unknown/Enemy Within (Firaxis/2K Games)
(2013) The Bureau: XCOM Declassified (Irrational Games/2K Games)
(2015) Chaos Reborn (Julian Gollop/Snapshot Games)
(2016) XCOM 2/War of the Chosen (Firaxis/2K Games)