Share your hidden gems that are currently in sale in Steam

Fhtagn! - Tales of the Creeping Madness and The Yawhg are both similar in style - choose-your-own-adventure games.
Flat Heroes pleasantly surprised me, highly recommend if you have someone to play local co op with.
Hotel Sowls is only 20% off but it's a cheap, really pleasant P&C adventure.
Sidewords if you like word puzzles.
Under Leaves for a cute, relaxing hidden object game.
Forgotton Anne is less "hidden" than some of the others but still very underrated.

Some not very well known indies off the top of my head

Teleglitch is a roguelike with neat-looking, unique visual style even though it looked like simple pixel-art to me at first. Also the ammo management in it is fun

Why Am I Dead At Sea is not actually on sale, but it's pretty cheap even on full price. You get murdered on a boat and now have to possess people as a ghost to talk with other people and investigate. Interesting characters, great soundtrack(it's by the person behind some of the tracks in Katana ZERO, and these were great as well)

Wayward Souls is an action-RPG from the devs that made Death Road to Canada, it's one of the rare mobile games that are actually good and P2P, without microtransactions, and eventually it got ported to PC. It can be really hard at times(or I just need to git gud)

Linelight
Gloom

https://store.steampowered.com/app/73170/Darkest_Hour_A_Hearts_of_Iron_Game/

Knytt Underground is on sale, it's my favorite game so I have to share it.
It's a little puzzle-platformer with exploration mostly and full of secrets. Atmosphere and music are really great.

Really good jrpgs that are on sale

Dragon Star Varnir
https://store.steampowered.com/app/1062040/Dragon_Star_Varnir/?curator_clanid=32763017
Death end Re;quest and Death end Re;Quest 2 are also On Sale
https://store.steampowered.com/app/990050/Death_end_reQuest/?curator_clanid=32763017
.hack//G.U
https://store.steampowered.com/app/525480/hackGU_Last_Recode/
Tales of Vesperia is really cheap right now
https://store.steampowered.com/app/738540/Tales_of_Vesperia_Definitive_Edition/

Survivalist and Survivalist 2
https://store.steampowered.com/bundle/15248/Survivalist_Bundle/

Starpoint Gemini series, minus SPG3.
https://store.steampowered.com/bundle/3781/Starpoint_Gemini_Franchise/

https://store.steampowered.com/app/548430/Deep_Rock_Galactic/

Deep Rock Galactic. An insanely fun, charming and atmospheric co-op FPS that somehow got overshadowed by Risk of Rain 2.

It plays not unlike the likes of Left 4 Dead and Payday, being mission-based with clear objectives, but each mission is set in a procedurally generated and almost entirely destructive cave system. And you fight bugs crawling all over the walls.

Also, it has dwarves. Rough, rude, drunk dwarves.

It's the kind of game that makes me wish you could nominate in multiple categories for the Steam Awards. Better with Friends, Best Soundtrack, Labor of Love and of course Game of the Year.

3030 Deathwar Redux - A Space Odyssey
https://store.steampowered.com/app/464360/3030_Deathwar_Redux__A_Space_Odyssey/

https://store.steampowered.com/app/250680/BELOW/

Bioshock: The Collection - full collection (including Bioshock 1, 2, remastered 1-2, infinite, DLCs) is cheaper than "Season pass Bundle" (Infinite + DLC). You can check it in the page higher. Or just go to BIOSHOCK: THE COLLECTION and compare with BIOSHOCK INFINITE + SEASON PASS BUNDLE

https://store.steampowered.com/app/616110/SPACEPLAN/
It's an idle game with story few hours is usually enough but i played for 20 hour lol
It's have an smaller(demo) web version to
Not sure about currency but it's should be cheap/very cheap i guess

https://store.steampowered.com/app/1292010/Missile_Command_Recharged/
Fire missiles to protect your bases! A classic arcade game's back and recharged!
A classic from Atari Inc
https://en.wikipedia.org/wiki/Missile_Command

I played this recently and really liked it, dumb but fun:
https://store.steampowered.com/app/514310/SENRAN_KAGURA_Bon_Apptit__Full_Course/

A Robot Named Fight! remains my desert island game. Steam says I currently have 698 hours of play.

It's a procedural metroidvania done correctly. There's tons of unlockable items, but no persistent stat upgrade nonsense. The key items themselves vary instead of merely their order of acquisition. Even the biomes have alternates so you're not stuck running through the same environment permutations all the time. A casual run takes less than 2 hours and you can save if you have to quit. The game released in 2017, but the developer has continued to make updates.

A Robot Named Fight! https://store.steampowered.com/app/603530/A_Robot_Named_Fight/

My review from multiple updates ago: https://steamcommunity.com/id/ACWraith/recommended/603530

Va-11 Hall-A an absolue gem where you play a bartender and meet a whole cast of amazing characters. You actually have to do the drinks, failures are as interesting as success since the game has a lot of Easter eggs as well as secrets which don't necessarily unlock by doing things right.

2064 Read only Memories curious about Jill's boss and want more lore related to Va-11 Hall-A's universe? This one game should help you to wait until the next release as this game happens a few years before Va-11 Hall-A and a few cameo characters come from it.

You already played those two and need something to pass time ? 🔴 Circles is for you ! Guide a circle to another circle, easy ? Expect needing to stare as your small dot as rules are added making the game increasingly difficult as you progress through it.

While you're at it, give a try to Flood of light a puzzle adventure with original mechanics. In fact, if you find a game similar to this one, send it my way, I would love to play another one.

I can't stop there without speaking of Bright Paw, a puzzle adventure where you guide Theo, the family's white cat, as he runs after the murderer of his family. Expect good puzzles, excellent voice acting, beautiful story and plot twist left and right. The game isn't currently in sale but worth every $ you'll pay for it.

Celeste

https://store.steampowered.com/app/361230/Super_Daryl_Deluxe/

I went into this game expecting nothing, and I got THE most interesting game I've played in recent years. Story is great, the music is superb, the artstyle, the characters... the only thing that kinda sucks about this game is that it can get a tad bit grindy near the end, but even that wasnt much of an issue.

https://store.steampowered.com/app/245280/ENSLAVED_Odyssey_to_the_West_Premium_Edition/

https://store.steampowered.com/app/742520/Astrologaster/

Funny little gem, nothing similar !