DOS

The Terminator: Future Shock

Wouldn't Marathon, which came out the previous year be the first fps with freelook? This may have been the first first-person shooter with full 3D graphics, though.

I'm pretty sure System Shock was released before 21th of December, 1994. Then there's CyClones too.

Neither System Shock nor CyClones featured freelook, as in moving your mouse with your head.

What would you call the aiming then? I only know three games (Operation FlashPoint being the third) using that kind of a system and I always thought Freelook's the correct term for it.

So freelook's the same as mouse-aiming?

As I understand it, "freelook" stands for an ability to "look" "freely" in any direction you want, as opposed to Doom and other early FPS where looking up or down was rather horrible and absolutely impractical.

In System Shock together with CyClopes the mouse was used to independently move the crosshair in limits of the direction you're facing. So, you can see that if used in such context "freelook" term appears to be rather meaningless. You can aim independently of your movement, true, but you can't freely look around.

I've never played the first Marathon, but I remember the second being on a similar ray-casting engine than Doom is, isn't this true?

Yes, it was on a somewhat more capable engine then Doom though with support for things like bridges and looking up or down.

I really need to check upon them, weren't they published as freeware some time ago?

Aye

http://trilogyrelease.bungie.org/

With Aleph One, you should be able to run it on just about any OS.

http://source.bungie.org/

You have to download a "scenario," or a port of Bungie's Marathon files to Aleph One, but I believe those are all on the second link also.