Starsector: It’s an Elite style open world space game. What makes it special is that it’s been in constant development for over a decade and has a crazy number of ships, weapons, lore and features. And a vibrant modding scene.

Also the devs are vehemently against DRM, so the only place you can buy the game is their own website. Or not buy. They put the full version up for anyone to download.

Shadows of doubt is a sandbox detective game. You are a detective and you have to solve crimes, which are totally randomized. What makes this interesting is that the world does not stop:

• the NPCs actually have daily routines
• the murderer might not stop killing
• you can talk with anyone
• and so much more

It is truly a sandbox! I havent played it too much yet, but i feel if i really start playing it, then i will skip going to bed!

Signalis

Antichamber

Cave Story

The Beginner’s Guide

Uplink

Hypnospace Outlaw

Exit Fate

The Red Strings Club

Oolite

LocoRoco (not an indie gem but forgotten)

Unciv for Android. It’s basically Civilization 5, but FOSS.

Shoutout to Iji, too. Amazing soundtrack and lots of replayability. It’s an old game by now, but it’s also free. Sidescrolling platformer, killing is optional.

Assault Android Cactus. Dunno how well known the game is, but it’s one of the best twin stick shooters/bullet hell I’ve played, with the android girls full of charm.

Gunpoint. Story based detective game where you solve a murder. Gameplay mechanics make you feel like a badass. You can pretty much finish it in a single sitting but its great.

Heat signature. A stealth based top down bounty hunter game with roguelike elements. Really well done. Made by the same guy that made Gunpoint.

Neo scavenger. A murder hobo roguelike with a surprisingly long storyline.

Super house of dead ninjas. Great fast paced platformer where you’re a badass ninja. Great to pick up and play in short bursts.

Fez. 2D exploration platformer with to change the perspective. Pretty chill and has a cool art style

More well known games that I’ll list anyway in case someones looking for some awesome ones:

Super meat boy

Project zomboid

FTL

Celeste

Crypt of the necrodancer

Enter the gungeon

Spelunky

Noita. Saw it mentionned in this thread and I am seconding this. Great game. But brutal as fuck.

Cave story. A classic. And it’s free.

Owlboy. Took the developer like 10-15 years to make. I’ve heard good things but I’m only just starting to play it.

Also pro tip: if you want more recommendations go look at what speedrunners are playing. People that spend that much time playing a single game over and over generally choose very good games to play.

Antichamber is hidden gem or simply forgotten? I don’t know how much attention it got in its time.
It’s a puzzle platformer but I was feeling my brain bend the whole game. And at the same time I never felt like the new mechanic was explained too little or something was artificially dragged out. Very good design.

IMO it was better than Portals

Phoenotopia: Awakening – an amazing metroidvania-related game. Relatively more popular than the other games I list, but is honestly one of my favorite games of all time.

Vision: Soft Reset – a metroidvania, but you can travel backwards and forwards in time and this really matters for gameplay.

Bombe – Minesweeper, but instead of solving the puzzles manually, you create rules (“if there is a cell with the number N and there are N empty cells around it, mark them all as mines”) which the game applies automatically.

SOLAS 128 – a puzzle game where you redirect signals in a huge machine, just a great experience if you like puzzle games.

Shadow of the Forbidden Gods - a strategy game where you play as the ancient cthonic entity waking up because the stars are right. Set in a fantasy world where the forces of good slowly become aware of the coming apocalypse and attempt to forestall your return. You have to get past the janky UI and some dreadful AI art, but the gameplay is unique and satisfying.

Citizen Sleeper - From the same publisher as The Pale Beyond, it’s another one of those story games that borders on visual novels. It’s a game about precarity and personhood set on an anarchic, decaying space station. Gorgeous art, fantastic soundtrack and it’s uniquely hopeful. Might be favourite game of the last few years.

It’s old enough that I can’t attest to how hidden it was/is, but Superbrothers: Sword and Sworcery is likely the greatest 3 hours I’ve spent in a single videogame. It’s chock-full of confidence and style and atmosphere. The story is nothing unique but the presentation is everything. Pixellated graphics contrasted with vivid sound design and a glorious soundtrack. I love everything about it.

Mindustry

Parkitect - an amazing RCT spiritual successor with cute graphics, some new mechanics (covering operational buildings and logistic routes). I have 100+ hours in it with my wife. It’s such a chill experience.

Nine Parchments - its a dual stick isometric shooter with wizards and elemental spells from the creators of Trine. Great co-op, unlockable characters/spells and creative mechanics. You can combine elements and the spells affect everyone, so for example a poorly placed healing spell can restore enemies health, or a misplaced fireball can hurt fellow players. Great fun!

Wildermyth - turn-based rpg with multiple characters and bite-sized modular quests and random encounters. The storytelling is simply amazing and each campaign plays out over a certain amount of time. The heroes age, retire, their kids can become adventurers as well. They can fall in love, compete, or based on the player’s choices even become other creatures or die heroic deaths which will also change how the story plays out. The art style is really nice and unique. I had many hours of fun with this one.

• To The Moon: Absolutely heart breaking.
• Tales of Maj’Eyal: An incredible rogue-like with 30+ classes and God knows how many achievements.
• Cataclysm Dark Days Ahead: Apocalyptic rogue-like. Zombies, bandits, aliens and Lovecraft shit. Want to raid a dojo? Learn Judo from a book and proceed to race around town on a pair of rollerblades practicing on the undead? Feel free.

They are hidden, so I don’t know about them. Sorry I couldn’t be of more help.

In decreasing popularity (estimated by me):

• Creeper World: A mix of tower defense and rts (with pause function) against a ever expanding goo called creep. The fourth installment is 3D and the next one will be a side-view spinoff.

• Tales of Maj’Eyal: Quite popular among the people who are into traditional roguelikes, but I very very rarely see it mentioned outside that community. It’s definitely the (nearly) traditional roguelike I put the most time into thanks to its class/ability system that bridges the gap between roguelike and turn based rpg really well.

• The Captain: Technically not indie as it was published by Tomorrow Corp (of World of Goo/Little Inferno/etc. fame) instead of the devs themselves. A mix between old school point and click game, but as a highly episodic space adventure. You travel from planet to planet on an overarching mission and each planet has its own interactive short story. Some are longer, some are very short and you never quite know what you’ll find before you land. All of the short stories have multiple endings depending on how you tackle the moral dilemmas it throws at you.

• Infinity Wars actually released before the rise of Hearthstone and also before the popular Avengers movie of the same name. It is to this day one of my favorite digital TCGs, and I played so many of them. Before I get into the main thing that I love about it, I wanna mention that every single card’s base version (colorless) is free, anyone can build any deck for free the moment they pick up the game and be 100% competitive with everyone else. The only thing they monetize is bling. Unlike in most mainstream TCGs both players do their turns at the same time in secret, once they both lock in, their moves play out. This gives way for some insane mindgames and outplays that eclipse those in any other TCG I’ve played. It is a bit rough around the edges, so it might be more of a “hidden diamond in the rough” than a hidden gem.

• Bombernauts is a really fun party game. To sum it up in one sentence: “Imagine if Bomberman was a platform fighter.” If you have friends to play with it, buy it on a sale, crank powerup drops up to the max (they stack, which took us hours to figure out), maybe download a mappack and I’m sure you’ll have a blast if the trailer looked any fun to you. There’s virtually no chance to play it with strangers through as it is super dead.

• Lastly I wanna give a shoutout to Clonk. Clonk is (or was) a 2D sidescrolling game-series that is visually reminiscent of Lemmings. The gameplay is a sort of mix between Minecraft or Terraria (predating it by many many years) and very very very low-pop RTS. It’s a mission based game where you control around 1-3 Clonks (the lemmings) and has full online multiplayer support. The missions can range from “build a base in this active volcano”, “take out the enemy team’s castle”, “win this wizarding duel” to “build a bridge across this canyon”. What made it truly unique was the community and community creations though. It was created with the explicit purpose to be customizable and users made many, many different maps and modes. It was to me what Minecraft was to the kids in the generation after me (without all the content creators, of course). Some people made an entire RPG in it. Others made what was essentially Among Us, just to give you an idea. Sadly the spiritual open source successor Open Clonk could never recapture the magic for me, and I guess I’m not alone in that because it pretty much died around 5 years ago. If I could make one game popular overnight, it would be Clonk. It did warm my heart to see that some of the celebrated custom map/mode creators from back then ended up getting into gamedev. One of the games developed by someone I remember from back then is Vintage Story.

Holy fuck I rambled a lot about Clonk and I still feel like I’d have so much more to say but this isn’t the most fitting thread for that.