I'd probably also have to go with Gore. I've played many obscure FPS games over the years but one that is truly forgotten AND actually pretty good is Gore.

There was also Deadhunt, another arcade FPS which is really just simple action in equally simple arenas. It's very humble compared to the likes of Serious Sam and Painkiller (or even Gore, for that matter) but it's interesting in that it's more like a first person version of Crimsonland and thus plays quite differently.

Shit, I think I'm getting it now.

Strife and Shogo are two good ones, but they're both sold here so I don't know if that counts as obscure.

I'm a fan of Malice: A 23rd Century Ultraconversion for Quake

I, on the other hand, got it with a gaming mag. :D

Which was probably more expensive and no fancy box either.
I miss those days, I used to go bargain hunting with friends after school.. or sometimes during.

I only played the demo back in the day and absolutely loved it. Many years later I actually DID manage to get it digitally, from Bundlestars I think, but it seems to be completely gone from sale now. The sad part is that I never got the full version to run, I always end up with a black screen. I found some posts from people complaining about the same problem online but sadly no solution that worked for me. :/

Marathon 1 & 2 of course. Probably the first FPS I ever played. Today it's one of those forgotten classics that actually defined the genre, together with id games. The reason why nobody seems to know them is because they were release on a Macintosh. Oh and guess what this what Bungie used to make in those days.

https://en.wikipedia.org/wiki/Marathon_Trilogy

P.S. That's also the reason for my Avatar its the logo of the series.

Well, they came a bit too late the party and were too obscure to define the genre. Personally I only learned about those games rather recently and didn't play them too much. Playing them now they seem like decent Doom clones but nowhere near as good as the original. What's interesting, though, is how strong the Halo is in them. The series almost feels like a Halo demake.

When I played it, it was through alternative methods if you catch my drift.
Patched up and functional, all the way through the end. GG.

Time passed, things changed, I saw it on GamersGate and Beamdog (weirdly enough), but had no money, then it was gone.
:(

Hmm interesting that kind of reminds me of Vietcong, which is a very good thing.

It's slow as hell.

I'll echo Chasm: The Rift and Gunman Chronicles.

Chasm: The Rift
It have great atmosphere, map design, weapon feeling and enemies that feels right to be fighting then and there. Also I really liked the campaign/story progression it led you through somewhat like in Quake.

Gunman Chronicles.
Play the guns how you want them. There are several settings for the guns in the game making you play the game the way you like. It's a fucking extremely gamey feature that other developers seriously have to fucking start to use in their games. It's a hilariously good game feature. Doesn't hurt the game is about space cowboy rangers fighting dinosaurs and robots with an occassional AI. HOORAH!

Edit: Lights on Chasm. The way Chasm use light throughout the game is also one thing that impress me. It's something that enhance atmosphere greatly.

Off the top of my head? Gonna have to go with Kingpin: Life of Crime. A weapon purchase and upgrade system, AI hirelings, and a gritty, dark urban look. That game just oozes the last years of 90's game design.

Does XIII count as obscure enough ? It's one of my favorite FPS ever. Great design, great weapon impact (with the little comic-book vignettes), awesomely cartoonish yet somewhat serious (the original comics attempt to be), and gorgeous cell-shading. I love everything about this game, except its stupid cliffhanger. Don't end your games on cliffhangers, guys. There's a 98% chance you'll never do a sequel. And no, wondering what happens next will not assuredly compel people to fund your next game.

Apart from that, Nosferatu wasn't well known, but it's on GOG now. I loved its terrifying atmosphere. And, well, I suppose that Undying is well known too, and what it lacks in fright it compensates in poetry. But again, dumb dumb cliffhanger ending.

Anyway, loved these games. And I'm not really into FPSes.

Was Rise of the Triad obscure enough? It was actually the first FPS I tried after wolfenstein and the only game I've ever played in VR.

Soldier of Fortune

Chaser

Forsaken (more of a descent clone though)