I'm curious if there are any obscure mods that had unique gameplay but were completely overlooked and weren't played much by the multiplayer community, or were forgotten about due to receiving a lack of updates for a long time?

I was and am a huge fan of Gunslingers, a simple mod Ehibika came out with way back when and Russel updated later down the line. I'm realizing I actually have no idea if it's v6b-compatible these days, but the idea is just that everyone gets the same six-shooter revolver-- shooting someone up close is an instant kill, but damage ramps down quickly over distance and rapid-firing reduces accuracy. It's really basic, but wound up being a ton of fun!

It never really took off, though-- typically a few friends and I would have a server up on TSPG for a week or so and all change to cowboy names and have a blast, but although we would get some other folks passing through the servers, they never lasted long.

Can confirm that Gunslingers is a ton of goofy fun. You kind of have to steel yourself for getting out early a lot depending on playercounts, but it's simplistic and really enjoyable to figure out. I'm preeeeetty sure it's not currently available with v6b, but I might be wrong on that.

I personally loved Roll's Spring Cleaning which was our version of prophunt. I think it was mainly around during v4 or 5, and it wasn't around for very long, but it was a ton of fun to play. The best part was when you'd get an animated prop that looks like it's walking and try to blend into the scenery by walking as it.

Invasion was probably the first mode I saw really start to develop (and in turn the first to die) when I started playing. It was a lot of retextured Doom maps and Super Moby enemies that shot Crystal Eye laser beams, but I remember getting a small amount of fun out of it.

Talking PvE in general, Invasion (as a romantic concept) maybe has more staying power in my head than the more linear MMSP levels do, but I'd also probably need some bells and whistles to avoid getting bored of the maps once the challenge of beating them is over.

Nobody remembers CSCC. It was really cool.

I recall a mod that goes by the name tactical? Only seen like 2-3 people play the WAD.

i remember xover weapons, it was fun combining the elements together here

I could name so many tbh, but the ones i'll drop here that i liked are Team Sneaking, Justified Classes, and Neumodian.

(Tbh I'm not entirely sure about Justified)

I personally quite enjoyed Justified Classes, since I felt it felt more like playing as the Robot Masters than the more mainstream one.

Though I only play against bots and Justified had proper bot support so that helps a lot.

Sportsball was always fun. Football started as just 1FCTF with Instagib, but then the actual hugeass football field map got made, complete with an IG Break Dash weapon. Then there was Ra Thor Basketball, which lasted maybe two weeks but GOD what a glorious two weeks.

The old Silent Falling competitions were a ton of fun too, trying to hit checkpoints without falling far enough to trigger the landing sound. Kinda miss those weird competitions.