A handful more games that didn't make the list for one reason or another.
Chip's Challenge
A classic tile-based puzzle game among old-school Windows gamers, being distributed with several of the Windows Entertainment Packs back in the early 90s and having 149 stages to solve (as well as several fan-made level packs to add even more). However, it's technically ineligible by my rules, since the original release of the game was actually for the Atari Lynx three years earlier. Sorry!
(I could have put the two-decades-delayed Chip's Challenge 2 or its "spiritual successor" Chuck's Challenge 3D in their place I suppose, but... nah.)
With the advent of the internet came too many fan games and parodies to count, some of which are actually surprisingly good. Dong Dong Never Die (东东不死传说, more accurately translated as "Dong Dong the Immortal Legend") was one that caught the attention of the fighting game community, and for good reason - it's utterly ridiculous. Lifting its plot from Terminator and several of its music cues, character traits and special moves straight from Street Fighter and King of Fighters while using digitized stills of actors a la Mortal Kombat makes it a game with a lot of schoolyard charm. The end result is a completely unbalanced, incredibly silly game with no regard for copyright laws, but it's an absolute blast to play, especially with friends.
Garry's Mod
A sandbox toy that showed off how powerful and flexible the Source engine really is. Not only could you spawn and play around with models, enemies, and basically every prop from all the major Source engine games, but people have crafted machinima animations, entirely new games and roleplaying servers and basically anything else you can think of utilizing complex rigs and Lua scripting. Really fun to mess with, but not a game per se, which is why I left it off.
Gamebryo RPGs (Morrowind, Oblivion, Skyrim, Fallout 3, Fallout New Vegas)
Though every major game Bethesda has released since the early 2000s has been on consoles as well, the PC remains my preferred way to play them. The reason why is pretty simple - modding support. Not just to fix the numerous scripting errors and bugs left in by the programmers (though some of those can be fun), but to add new quest lines, weapons, perks, vehicles, recruitable allies, and whatever else you may want. With thousands available to experiment with, all of these games become a fresh experience each time you revisit and replay value is basically infinite.
Goat Simulator
A game that recognizes that janky physics can be quite a bit of fun in their own right, Goat Simulator just puts you in the role of a goat with a sticky tongue and sets you loose on a city to cause mayhem. You get a ton of achievements for doing various things - finding objects, blowing up gas stations, knocking stuff over or just driving people crazy, but you're by no means bound to any goals. The devs even acknowledge the fun of the jank, as it was their policy to only fix game-crashing bugs and leave the rest intact. They even added more modules parodying MMORPGs and the Payday games (having you prank people as a team of animals with various ridiculous talents), so if you just want a bit of good, absurd fun, Goat Simulator is the place to find it.
Mortal Kombat Trilogy
A multiplatform release from the tail end of Mortal Kombat's 2D era, its selling point was including everybody from the first three games (even the bosses) as playable characters. It did just that, but no real playtesting was implemented either, so it was a ridiculously unbalanced mishmash of nonsense; that's also what made it a lot of hilarious fun, though. The console ports all had some flaws - the N64 version lacked load times but had poor sound quality and several fighters missing owing to cart space restrictions, while the PSX and Saturn versions had everyone and higher-quality sound but rather atrocious load times (particularly in Shang Tsung matches, where the game would pause for several seconds and load mid-match every time you morphed). The PC version, however, was arguably the definitive release, having all the characters, high sound quality and, since it installed everything to disk, no load times either. So if you want some dumb, campy entertainment, track this one down and give it a play!
MUGEN
If you've been on Youtube watching gaming videos for any period of time you've probably seen at least one of MUGEN, a fighting game engine that lets you import your own graphics, build your own characters and tweak nearly all of its mechanics to your liking. Because of this, people have made literally thousands of characters to play around with - some attempting to be legit recreations of existing fighters, others original, and still others just meme-laden broken nonsense. People have even included stages from other games like Super Mario Bros as "fighters", so it's surprisingly flexible. But you really do have to put in quite a lot of work and hand-tweaking to set it up and it's not really much of a game in itself, so I opted against including it
Portal, Portal 2
I do love me some Portal. A action-puzzle game set in the Half-Life universe where you utilize the eponymous portal gun to sneak past obstacles, hop over long gaps, bridge two areas that otherwise wouldn't reach and do all sorts of other clever things to make your way to the end. All presided over by the twisted AI GlaDOS, who is both threatening and consistently hilarious. Unfortunately both games were also simultaneous releases on consoles and therefore disallowed by the rules I set.
SimAnt
After SimCity found enormous success as a "software toy", Maxis branched out the Sim brand into countless other areas, big and small. The smallest in scale but certainly not in depth, SimAnt basically serves as a virtual ant farm crossed with a real-time strategy title. You choose a single ant to serve as your personal avatar (who is always reborn shortly after being killed as long as the queen survives) and set out to help your colony thrive, collecting food and laying down scent trails to automate the behavior of other ants while avoiding hazards like getting stepped on, sucked into the lawnmower or eaten by antlions or spiders. You "won" by overcoming and defeating the red ant colony in the same patch of yard or, in the full game, completely eliminating the red ants from both the yard and house one square patch at a time. While SimAnt is a not terribly deep experience, it is fun to mess with for a bit, and once you get good at it you can beat the whole game in about ten minutes. In true Maxis form it also comes with an enormous 170-page manual, though only about a third of it talks about the gameplay and mechanics, with the rest being a lot of very well-researched ant facts.
SimCopter/Streets of Simcity
I mention these two not because they're good; quite the opposite in fact. They're very ugly 3D games that have mountains of unpatched bugs, esoteric coding that makes them almost impossible to run on anything but very specific hardware from the early 90s (or PCEm), and even then they crash frequently, sometimes bringing the entire OS down with them. But you know what? That can be pretty fun sometimes. As long as you're not set on taking them seriously, playing around with their insane physics models and uniquely janky mechanics, topped with Maxis's strange sense of humor, some unironically good soundtracks and a rather notorious Easter egg in Simcopter inserted by the programmer as a prank, makes these games surprisingly entertaining even with their enormous flaws. The guiltiest of pleasures, these.