Battletech should be the king of tabletop wargames. But no, everyone just wants to play 40k because of the sunk cost.

Simon the Sorcerer

It always seems to be overshadowed by Monkey Island. Personally I think it's actually better in many ways.

I thought Slice & Dice was going to take Steam by storm but it kinda just came and went. Amazing little roguelike dice battler

For video games, Full Spectrum Warrior.

It's got a unique third person-ish view where the player swaps between different fire teams or special units, and orders them. It looks like a third person shooter but is just a real time ground level tactical game. It's demanding but fun. It's the kind of game that Brothers In Arms, old school Ghost Recon, or Doorkickers players would love. I don't know why nobody really remembers it or why somebody hasn't made a spiritual successor.

Aotenjo Infinite Hands is like Balatro for mahjong. Strongly recommend it

Cattle Country, a completely unique stardew-esque game set in the wild west. It feels way more in depth and polished than Stardew, and you can be attacked by random wildlife and even outlaws lol

Would chess count?

I mean chess is not not popular by any stretch of the mind, a lot of people around the world are playing it every single day and that won't go away anytime soon, but I'm always surprised to see so much more excitement going on around a new version of This or That video game that people will play for a little while before switching to a newer version than for chess. Despite its apparent simplicity (and lack of visual effects), chess has remained a challenge for the smartest among us, and will keep on being so no matter how much better computers can be playing it.

star trek online and champions online. they were pretty reasonable for free to play mmo's and the costuming was amazing.

The Legend of Alan D'ar, it was for me the first co-op rpg I'd ever played. My brother and I couldn't out our controllers down. Sadly all you ever hear about it IF anything is how much people hated it.

Quake Champions is pretty great, surprised it's not at least a little bigger

Me and my girlfriend are big fans of Doomsday Paradise, a rouge like dating sim

For video games, The Touhou series.
Outside of the games They have alot of fangames/Fan Content ,a massive community and a popular Fan Song (Bad Apple).
Also Undertale/Deltarune has some inspiration from Touhou.

Shoot Shoot Mega Pack is extremely underrated imo. It's a really fun 2D shooter +party game, and it only has 13 reviews on steam.

RS isnt really popular outside millennials groups, although it's declining a lot last few years

For video games, Ostranauts. It's the perfect space survival sim IMO. You wake up on an industrial salvage station and get a ship. Then you fly to derelict ships and scrap them for money and parts. Build up your own ship and travel farther and farther out. It's jank as fuck to learn but once you get it down it's the type of game where you put on music then just go for hours and hours. It's early access and a lot is changing but the core gameplay loop is so addicting already.

For tabletop games, Infinity. It's the best miniatures skirmish game I've ever played. The rules are deep but tight. The number of minis you put on the table is just right to me. List building is the best of any game I ever played. The rules are free. The app is free. The miniatures are the best out of any wargame I've ever played. It's just a shame that people are so locked into Games Workshop that they don't see other games as an option. Like I had a couple friends get hardcore into it but never more than that. And at the height of it's popularity at our store we had one of the best players on the East coast play in a tournament. That was a sight to behold. Like I'm not a tourney player at all for any game. Watching the number 1 east coast player do his thing was the most inspired I ever was to become a tournament player.

Meinkraft