Do flash games count? Motherload is great.
It’s been a few years, but Armagetron Advanced was the best. Felt like you were riding the lightbikes from Tron.
Warzone-2100
OpenTTD
I often revisit Soldat
I’ve played Simutrans on and off ever since the mid 2010’s. I’m not any good at it, and usually play it without regard to a lot of its mechanics (especially managing finances), but I’ve spent countless of hours just connecting communities and cities with over-engineered roads, rail systems, ferries, and airplanes.
Lost Vikings
Clonk! It’s a 2D mining/strategy/base-building hybrid that was apparently more popular in Germany than other places. I actually paid to play it way back in '05, but it has since become freeware. It’s got a particle sim (similar to Noita, but not as extensive) that plays into the scenarios well.
Nikujin by ikiki, and other games by the same developer. Not sure where to find them now, but they were some of the greatest freeware games I have played.
One of my absolute favorites is a quirky strategy game named Lord Monarch. I found it on the Nihon Falcom website way back in the mid 90s when I was first starting to use the internet: Lord Monarch
It’s super tiny in modern terms, but I remember waiting a good 20-30 minutes for it to download from a 33.6Kbps modem.
Another huge one for me was a game I actually got a full version of from a Gravis gamepad promo CD named Seek and Destroy. It’s a top down shooter where you can be either a helicopter or a tank: Seek and Destroy
The last one that comes to mind is a giant robot fighting game that also came on that same Gravis CD named One Must Fall: One Must Fall 2097
Haven’t played recently, but this one came to mind’
I missed the original, but Scorched 3D was a big hit at my high school.
For the longest time I thought Minecraft was free because I only ever pirated it. Lol
PlanetSide 2 is the free-to-play I keep going back to
Heck, I still pirate it even though I bought it. (I didn’t want the hassle of migrating my account after the Microsoft buyout.) PollyMC ftw!
Wolfenstein Enemy Territory, or the modernized remake, ET Legacy
Neat! I had a ton of hours in ET, played competitively for a while, and made some silly mods for my clan.
UnReal World is a free, survival-focused roguelike rpg that came out in 1992 and is still actively being developed and improved. It’s got a lot of depth and a very cool fantasy setting heavily inspired by Finnish folklore (the developer is Finnish).
I highly recommend it if you’ve got the patience for an in-depth roguelike rpg.
I don’t know if it technically counts as freeware, but Space Cadet Pinball. Back on XP it was my go-to for something quick to play on the offline computer, and I just brought it with me to every new machine. Also it’s now been decompiled and will run on pretty much anything!