Guys! I found a very unknown old-school fps. It's called Rebel Moon. Sadly it doesn't use the Doom engine, so I won't be able to instantly play it unless there's a TC out there. But yeah, a very rare fps. :D
I looked it up and it doesn't look terrible at first glace. Apparently you could get it only by buying a specific line of 3D accelerators, so yeah, no wonder it got lost to time. Still, seeing an early 3D accelerated game is always interesting IMO.