The missing link between X-Com and Warhammer 40K. Yes, you heard that right. Those two IPs share blood in the development sense.
You see, back in the day, before X-Com, before Warhammer 40K, there was a tabletop skirmish game called Laserburn.
Laserburn contained a lot of things you might recognise - beyond just the rules for futuristic combat, it also had an Imperium, power armour, bolters, lasguns, dreadnoughts, etc.
Now, Laserburn directly contributed to two important things:
Its creator went on to become one of the founders of Games Workshop, where its general concepts would be re-implemented into the game Rogue Trader.
At around the same time, Laserburn was adapted into a video game: Laser Squad, by Julian Gollop.
Laser Squad was a hit, and its gameplay and lore elements would go on to be refined and enhanced by Gollop and his team into its own effective sequel, UFO: Enemy Unknown, also known as X-Com: UFO Defense in North America, the first game in the much-loved X-Com (now XCOM) series. Rogue Trader, meanwhile, would be updated and re-released as a second edition, from that point on taking the title Warhammer 40,000, which would go on to have multiple updated versions and spin off many games in both the tabletop and video game domains.
So now you know! With this all said, it's probably not surprising there's at least one big 40K mod for OpenXCom.
(Final note: It's annoying that the display format for these stories removes all paragraphs. GOG, Pls fix)