Nexus: the Jupiter incident. It is a now a bit old tactical space combat game with a big focus on the narrative. It's awesome, but I never see it mentioned anywhere.

Megabyte Punch is a side scrolling fighting game where you build your robot with different parts salvaged from fought robots that give you different abilities and powerups.

It is a super fast, casual game that you can bang out in a few nights. It has a pretty good electronic soundtrack, boss fights feel weighty even if they are relatively simple.

One of my favorite games as far as just fun and de-stressing!

I recommend Scavenger SV4 It's a very unique game where you send a rover down to a planet to grab what alien artifacts you can before your radiation exposure gets past the point it can be treated. You can bolt some of them onto your rover to make it better and send it down again. It also has several hundred different endings that are decided by how much radiation you absorbed and how much loot and what loot you brought back.

Bugvasion TD (9 reviews)

It's a charming little tower defense game where you fight bugs with very fun abilities. I also play tested it so I may be a tad biased but I think it's underated and fun :3

Dink Smallwood is an old fantasy role playing game. It has a small community that makes mods for it. It's really dumb but it's free to play and very short if you have nothing better to do.

edit: Wow! I didn't realize a lot of people here know this game. That's actually cool.

Minishoot Adventures is a twin stick shooter with a 2D Zelda-style map.

One Way Heroics+

Semi-Rogue-like RPG, flee away from the darkness on the leftside of the screen, try and defeat demonlord and save the world. (Multiple endings)

One of my favorite games ever, guy made his own engine.

It does have design flaws, don't get me wrong. But this is is really novel and has enough content to get somewhat deep into it.

Eventually you start seeing the same things but for essentially a one man team it's really impressive.

Voices of the Void a free (likely while it's in pre-alpha) light simulational game about receiving outer space signals and recording them to sell. You use the currency to clean up, upgrade, and decorate your small facility while moving around the Swiss forest valley you're in to repair and upkeep the satellite dishes that make the operation function.

It sounds very purely simulational, but there are a lot of secrets and interesting signals that are more than signals. It's also an Unreal engine game, but features a lot of Source engine love, for example the art style is reminiscent of Half-Life 1, all of the sound effects are EXTREMELY Source game nostalgic, and there's crouch jumping.

To me, Ctrl Alt Ego is not well known enough. It is an immersive sim in the style of Prey. You play as a robot roaming a station, where your Ego (like a spirit) can pass into and control all sorts of objects to solve puzzles, evade, control or kill enemies. The graphics aren't impressive (it was made by a 2-person team) but the gameplay is so interesting and the story is surprisingly compelling and funny!

Automachef is the most unique factory game I've ever played. You make factories to handle food orders, try to reuse as many parts as possible to save cost, figure out how to handle massive rush hour mobs without burning too much power or dropping orders, and so on.

Down the line, this game has its own coding language for controlling machines and handling orders. It's got a puzzle campaign, and a whole contracts mode, all around a good time. You can make VERY tight factories, especially with late game tech.