Linux
Linux (or GNU/Linux if you're nitpicky - and be sure to pronounce it correctly) is a family of free Unix-like operating systems.
Even though its desktop presence is still modest, Linux is immensely popular in pretty much every other field: smartphones and tablets (as Android is derived from it), netbooks (as Chrome OS is also derived from it), handhelds (as the Steam Deck runs it), embedded devices, internet servers, scientific supercomputers, corporate mainframes, graphics renderfarms, and so on. Now that Windows is literally spyware that forces you to use online accounts and sends still good machines to the landfill with arbitrary system requirements, and Apple's machines are as overpriced as ever, you are well advised to look into this.
Now you may ask: "Sure /g/earheads love this thing, but what about the vidya?" While Linux has far fewer native games than Windows, there is Wine: a compatibility layer to run Windows applications. Valve uses their variant, Proton, to deliver Windows games to Linux systems seamlessly. At this point, most Windows games without kernel-level anti-cheat will run fine; check the Proton compatibility list. Wine by itself can be complicated to use, but the community has developed various tools to streamline it: Winetricks can install all the .NET and Visual C++ redist mumbo jumbo for you, Heroic and Lutris handle games from GOG and Epic, and frontends like Bottles and Q4wine handle standalone programs with local installers.
"But is Linux actually usable by non-super-nerds?" Yes! Linux is much friendlier these days, to the point it's not really harder to use than Windows. Still, the sheer amount of options can be intimidating. For a start, which distribution do you choose, out of hundreds of options? Let's make this simple: for general use, go with Fedora KDE or CachyOS. For old and low-end PCs, check Lite, MX, or Q4OS. For extremely old and low-end PCs, try Damn Small or Tiny Core. For a handheld or a living room gaming box, go with ChimeraOS. And for a retro emulation box, especially Arm-based mini-computers, go with Batocera. Don't be afraid to experiment, as any of them should be fine for newbies... No, not Gentoo!
The games
Note: These lists include only games with native Linux ports (or old DOS games sold wrapped in DOSBox). Wine and Proton can run a vast number of Windows games, but they won't be included here because testing all of them would be an insane amount of work. So again, check the Proton compatibility list.
Free games
Commercial games
- Adventure games (includes survival horror)
- Beat 'em up games
- Fighting games
- FPS games (includes TPS, 6DoF shooters)
- Platformer games (includes action-adventure, metroidvania, run n gun)
- Puzzle games (includes puzzle-platformers)
- Racing games (includes vehicular combat)
- Role Playing games (includes Action-RPG, roguelike)
- Shoot 'em up games (includes artillery games, top-down arena shooters, rail / tube shooters, space trading shooters)
- Simulation games
- Strategy games
- Others (includes sports, visual novels, multi-genre compilations, casual games, experimental / art games, retro games)