Machinarium - imo, one of the coolest adventure games I've ever played. Perfect combination of game and art
Robot Alchemic Drive for the PS2. Giant transforming robots fighting monsters in a destructible city, what's not to love... Well, aside from the newscasters horrible voice acting. The game is very cinematic and has a fairly complex control scheme, which I think is what drew me in more than anything. Also, if you like games like Harvest moon and Stardew Valley, check out Shepherd's Crossing. It took me a while to get used to the game but once I did I sank a ton of time into it.
The Stanley Parable. Idk how common it actually is, but it's not exactly mainstream, and it's not your typical game.
Apotheon, it's a platform action game set in greek mythology and the graphics are in the style of the artwork on greek pottery. It's for PC and is on steam.
There are so many great MS-DOS games. Not so much unknown, but more forgotten. The Lost Vikings, the Commander Keen series, and Blood are some of my forgotten favs.
Crusader Kings 2 (also know to fans as Incest and Murder Simulator). Not sure if it counts as unknown because it's pretty popular on Steam, but most people I talk to have never heard about it, so close enough.
OpenSpades and Ace of Spades 0.75, those games are really nice and still have a community being around
Recently got into Beholder, not sure how well known it is. You play as a guy running an apartment building in a totalitarian government. It's fun trying to fugure out how to not get killed by either the government or your tenants.
Y E S also nihalumbra, which is a puzzle platformer with a dark atmosphere. And total carnage. It's this arcade shoot em up me and my dad played on this midway collection all the time. Sure it's violent and you fight a giant robot hitler head, but this is appropriate for my 6-8 year old daughter! Lol we had a lot of fun
Freedom Fighters - this TPS featured great AI on your companions in its time in my opinion. This game is simple and easy but had good aiming controls. its fun for an action game. Most may think this game doesn't deserve a sequel but I just want it to have one since it was a very great and fun TPS game for me.
I have that Midway Collection. When I was much younger I used to play Smash TV in the arcades a lot. It's basically the same thing as Total Carnage