Antichamber: The best puzzle game ever made. Absolutely mind-bending.
Super Mario 64: It’s from 1996, but its community has kept it alive and thriving over all these years. The fastest known speedrun of the game mixes computer science, physics, and parallel universes. People have also reverse-engineered its source code, and it has plenty of ROM hacks.
AAAAXY: It’s kinda like 2D Antichamber but open-source and a platformer. I initally disliked the level design, since the game often tempts you to try brute-forcing with pure platformer skills, but that’s actually the genius of the game. Almost always, there’s a slicker solution hiding and plain sight, and all you have to do is step back and use your brain, which is often trickier than you think when you’re fixated on grinding a tough jump (Except for the room “The Wide Gap”, which is pure evil and took me over 100 tries). I love the game’s sense of humor and there are also some nice math references. The best thing about this game is definitely the name. Second best thing? The soundtrack.
Baba Is You: This puzzle game broke my brain. The core concept of this game is that you can change the rules of the game, based on the current rules. It sounds simple, but some of the levels took me hours.
Kerbal Space Program: This game is a real blast! I learned more from playing this game during my high school Aerospace Engineering class than from the class itself. The physics could be more accurate though, such as using proper N-body simulations instead of the patched conic approximation, but it’s a good compromise between accuracy and difficulty. There are some pretty freaking crazy things you can build in this game, such as making a helicopter by attaching sideways rocket boosters to the tips of the propellers.
The Powder Toy: A sandbox game, except the sand can be uranium or protons or dozens of other crazy elements. It has multiplayer too.
Oh My Git!: It’s a game that teaches you Git, the version control system.