I've been discovering that despite what I originally thought - there exists a small collection of high quality games which are not only free but also developed openly.
I'll list the ones I have found to date, I wouldn't mind seeing any recommendations!
Mindustry - Essentially a fully complete indie game. You can buy it on steam to gain access to a few other features but nothing game changing.
Super Tux Kart - Literally Mario Kart.
Super Tux - Literally Mario
Luanti formerly Minetest. - A voxel game engine, you can add hundreds of mods to make the game into what you want, including into just straight up Minecraft.
Veloren - An open MMO, still very much in alpha development
Thrive - Spore on steroids, still in development although I've spent a good 20 hours having a lot of fun with where it's at, at the moment - with the bacteria stage mostly complete and the multicellular stage taking shape.
Unciv - just civilization.
One thing you probably notice with this list is there are a lot of games which are clones or essentially clones of other games. So I wonder if anyone knows of games which have their own unique style and ideas?
I'll probably post some reviews of each of these games and any more I find out about in separate posts.
Here's a Wikipedia list, but if anyone has any favorites rather than me just dumping a list of varying quality games on to this post.
Check out Freeciv by the way, a libre civilization clone. It's my personal favourite. As for games that aren't clones, there's an Android game called Doors of Doom. I've been thinking about making a game inspired from it for Linux, both mobile and desktop, but I'm not sure how I feel about it yet.
Not sure if Pixel Dungeon (and its derivatives) fit in this. They're released under GPLv3. But it's a complete game, and not a clone (though it follows the traditional roguelike genre).
In the same genre, check out Dungeon Crawl Stone Soup.
From the looks of it Pixel dungeon 100% fits the libreculture community, I'll it to my list to play and then review or you could write a review if you like - it would be cool if more people join me.
Ooh, there's also Shattered Pixel Dungeon, which I believe is a spin-off of the original. I could write a review, but I tried writing game reviews once before, and faced criticism for how poorly I had done it. Maybe I could consider trying again.
Well, there's the odd hybrid that is OpenTyrian. The code is GPL2 and the assets are separately available as freeware (ie. gratis but not free-as-in-speech). That puts it in the same boat as e.g. OpenXcom (free engine, nonfree assets) but makes it slightly cheaper.
Tyrian is a bit unique as a shmup; you don't immediately die when you get hit and you get to customize your ship. Development of the open source engine has been extremely slow (the last release is two years old) but then again the project just aims to be a modern implementation of one specific MS-DOS game and it does that job just fine.
Endless sky is really fun, and might scratch the same minmax itch as thrive.
Endless Sky is a 2D space trading and combat game similar to the classic Escape Velocity series. Explore other star systems. Earn money by trading, carrying passengers, or completing missions. Use your earnings to buy a better ship or to upgrade the weapons and engines on your current one. Blow up pirates. Take sides in a civil war. Or leave human space behind and hope to find friendly aliens whose culture is more civilized than your own.
One of my favourite games out there - not just open source ones specifically, but like all games included.