Alien Quake Total Conversion
This modification for id Software's Gothic first-person shooter is probably one of the most controversial and hard-to-find (if it's anywhere online at all) out of all Quake-based mods. But it was also one of the most awesome conversions at the time, appearing sometime after the game went retail. Players found themselves fighting against Quake's typical opponent AI, but with Alien-based skins. The environments brought total immersion, full of dark corridors and the lurking monsters we've come to know and love. The mod quickly became popular and was soon a hot, free download packed with 11 levels (plus a secret level), new weapons, enemies, textures, sounds, and more.
Eventually, 20th Century Fox took notice and swung its almighty Ban Hammer at the authors. "The Alien Quake project has been discontinued by 20th Century Fox," the mod's author wrote in a statement. "I received an email April 11, 1997 from a 20th Century Fox representative that ordered us to cease all activity. The Alien Quake project was using copyrighted material without permission and this makes Alien Quake an unauthorized and illegal production."
Wait. It gets better: "Therefore, you are hereby ordered to remove all your Alien Quake files from your computer storage. You must also remove all references to Alien Quake from any WWW pages or Internet sites you keep or maintain. All distribution of Alien Quake is illegal and you should know that the Alien Quake team is under obligation to report the name and URL of any distributor to 20th Century Fox. Please let us know if you know the URL of a distributor or potential distributor," the author wrote.
20th Century Fox released (the original) Aliens vs. Predator PC game a few years later.