The best open-source games you know

Mindustry is a really fun automation/tower defense game
- Second Mindustry, I played it up once and it was great. Basically Factorio for phones.
  
  thirded. played it years ago and got into it again recently. you should check it out again, there's a lot of new stuff they've added.

Did you guys tried Endless sky? Awesome game if you love space
- And minetest+mineclone2 is pretty good if you want to play minecraft but don't have a license
  
  Minetest in general has such a good mod selection it’s insane! My siblings and I never fail to have a good time goofing around with the plugins people have created.
  
  Thank you for this! I have already logged hours playing with my kid since seeing your suggestion. We have only played mineclone2 so far. I will look into veloren next.
- Such a great game.
- Came here to mention Endless Sky. Great game!
  Don't be misled if you were a fan of the old Mac games Escape Velocity or EV:Nova, Endless Sky is inspired by/derivative of EV but is not the same and you'll (well, I did) find out the hard way that the old strategies don't carry over.
  
  I grew up playing the EV series and I love Endless Sky. Is there something about the clone that you don't like? I can't thing of a change that I dislike. For example, fleet management is improved. Being able to dock your various ships and escorts is pretty cool.
- I recently got into that game quite a bit. Playing it on steam. Just the other day I discovered I can board pirate ships and kill the crew to claim the ship as my own. That has been a significant power boost for me and really unlocked the game.
  Even before that I was having fun trying to survive with limited power while still exploring the world

OpenTTD is good
- I love that game. I've put so many hours into it
- I love OpenTTD, came here looking for it.
  For the uninitiated, it's a reimplementation of Chris Sawyer's Transport Tycoon Deluxe. Build a transportation empire of trains, lorrys ships and planes.
  There's also a modern spiritual successor in Transport Fever (commercial, not open source)

Beyond All Reason is AMAZING. I can't say enough about it. Its my favourite game, and totally annihilates (!) the competition.
Though I guess the competition is pretty small for large scale RTS. Maybe:
Total Annihilation
Supreme Commander
Ashes of the Singularity
Sins of the Solar Empire (sorta)
BAR has fixed all the UI/UX problem, scales well, has a big community, is free, fun, and super deep and complex.
- I don't really like this type of games but the game looks pretty cool
  
  Yeah its a specific type of person that would enjoy it, perhaps a Factorio/Factory Must Grow genre mixed with small scale RTS.
  Still, playing 20v20 games are incredible.
- Also ZeroK, on the same springRTS engine
  
  Zero K is also great, but they've changed the gameplay a lot from the original TA
- Had too scroll way too far for BAR. It’s amazing!
  
  Its also gone gangbusters over the past few months, unsure why. Hundreds of concurrent players at any time which is pretty amazing.

Shattered Pixel Dungeon ! And its origin, Pixel Dungeon.
A really nice rogue-like, among the best Android games I know, it’s still fun after all those years and very actively developed !
- Great classical roguelike
- Would love to checkout the code for this thanks for the suggestion
- You can also fairly easily get Shattered Pixel Dungeon to run on a PinePhone or PinePhonePro!

Cataclysm DDA Is THE open world zombie survival experience. So long as you like obtuse roguelikes with nearly no graphics.
Although Im obviously biased what with being a dev and all.
- CDDA is mind bogglingly cool. I play a weekend of it every few months. I know it won't ever happen, but if it got the Dwarf Fortress Steam treatment one day, it could be the last game I ever bought and I'd be happy.
  
  I'll just leave this here ;) https://store.steampowered.com/app/2330750/Cataclysm_Dark_Days_Ahead/

I will say that 0 A.D. and veloren are my favourites!

Veloren is inspired by games such as Cube World, Legend of Zelda: Breath of the Wild, Dwarf Fortress and Minecraft.
You can play single player or multi-player, standalone or use an online server, or even host your own server in a Docker container, or on a Raspberry Pi. Plenty of options!
You start by creating your character, you can collect items for your inventory, you can craft items, there are weapons and combat, you develop skills, can tame creatures, you can trade with merchants, you can socialise, and lost more. There is no single, specific goal or focus, and the idea is to keep exploring and have adventures.
The game is community driven and actually updates quite regularly.
It is clearly no clone of Minecraft. It is fun and adventure!
See https://veloren.net/
- Totally agree, one of the best open-source games ever

Beyond All Reason
https://www.beyondallreason.info/
It a grand scale RTS game with robots and insects loosely inspired by Total Annihilation.
- Holy shit, this looks awesome! Maybe I can scratch that TA itch.
  
  I've really enjoyed it.
  If you like Supreme Commander, you will be sooo very happy with this.

Have not seen anyone mention one of the best rogue like games out there, Tales of Maj'Eyal
https://te4.org
Base game is free to download and play from their website. Massive world, tons of loot, an incredible number of classes and abilities to combine, it's such a fantastic game that also has native Linux support.

Mindustry is an awesome strategy game that combines Factorio with tower defense.
Sonic Robo Blast 2 Kart (ridiculous name I know) is one of the most underrated games ever. It's a super polished, high quality Kart game with an insane amount of mods and maps. The online isn't that populated but the singleplayer time trial is TONS of fun. If you like hunting for medals, it can be a pretty deep rabbit hole. There's a sequel in development but no release date.
GzDoom is the most popular Doom source port and there's a practically infinite amount of user generated content. If you don't know where to start I highly recommend Doom: The Golden Souls Remastered and Castlevania: Simon's Destiny. They're good enough to be premium games.

Cataclysm Dark Days Ahead has been mentioned so I'll add OpenMW to the thread. It's a open source engine rewrite of Morrowind and requires the base game to run Morrowind but it has the potential to be used to create new games and the devs are looking to expand it to allow the creation of ARPGs as well.
Another worthy mention is Endless Sky, it's an open source game inspired by the classic space trading and combat game Escape Velocity.
- Endless Sky was surprisingly addictive to me, it really scratched the exploration itch. Sadly I played through most content at some point, so now I'm waiting for there to be enough new stuff for me to play again. I really enjoyed it, including the stories and lore and universe!
  
  I also played through most of the content at some point, but when they eventually updated with new content I couldn't get back into it. Maybe I should try again because that was such a fun game.
- Since you mentioned OpenMW I thought I should mention Daggerfall Unity. It's an rewrite of Daggerfall using the Unity engine, also requiring the original files. The best thing about is that the developers have made it easily moddable and a very healthy modding community has sprung up for it, some of which really make the game feel like what the original developers were going for but had to deal with the technical limitations of the time.

Battle of Wesnoth. Haven't played it in a while, but I remember spending hours playing that at one point.
- And there are so many campaigns, it is incredible.

https://github.com/open-duelyst/duelyst
Duelyst was a very popular online card game that shutdown around 3 years ago. The developers have recently released it into the public domain (via CC0 license).
You can completely selfhost a private instance (repo has a good straight forward guide)
There is a public instance available to try https://duelyst.org/. Though it might be pretty barren.
There is also a closed fork which should have a more active userbase https://duelyst2.com/, the game rules are a little different (draw 2 vs draw1), but should have more users to get a feeling for the game.
The game in a nutshell is basically Hearthstone on a chessboard. It’s very fun and approachable and in my opinion one of the best cardgames right next to MagicTCG :). Hopefully the community for it will grow more and we can have a sort of second renaissance for it :)
- I seriously think that every online only game should have to make the server assets public if they've abandoned it longer than 10 years. So many good games are just lost to time.
- You have my attention

OpenRCT if you're counting that style of open source game
- I thought you needed to bring your own assets for that game
  
  You do, but the game logic itself is all OSS. It just requires you to buy the games in order to load the assets and scenarios. IMO it's a great open source achievement even if it isn't 100% pure open source. There have even been community additions like mods and custom ride types that really make the game even cooler.

CataclysmDDA is an amazing open source roguelike. Has a bunch of tilesets if you don't like ASCII
- Also most og roguelikes are open source which is great!
- What other game you can play as neckbeard otaku on a quest to become a real catgirl in the world infested with zombies and whatnot? God I love Cata

Cube 2 Sauerbraten is pretty good! Free arena shooter with built-in level editor
- The original Cube is also fun, at least as a singleplayer game and comes with a lot of SP maps. The SPMP (or MPSP, i don't remember :-P) mode also allows playing the MP maps with randomly spawned bots.
  The AssaultCube fork adds more realistic environments (relatively to the original game anyway), though it is fully MP oriented. But you can still play with bots.
  
  There are still people playing AssaultCube?

If you like RTS games similar to Total Annihilation, you should definitely check out Beyond All Reason, it's gorgeous and fun: https://www.beyondallreason.info/
- Another supcom similar is zero-k. Didn't know there were so many open source options!
  
  ZeroK uses the same engine as BAR, my game, and quite a few others. 😋 And yes, definitely should check out ZK, it's a mature project with a nice community and awesome devs.
  Recoil is pretty much the only foss engine purpose built for modern rts games of all types.
- Now there’s a name I haven’t heard in a while. I sank way too many hours into this (started off as a TA clone but branched off into other game modes too) a decade or two ago, and it looks like it’s still going.
  https://springrts.com/
  
  Spring is dead. The fork Recoil is going strong and fast. :-)
- This looks really cool. SupCom wasn't quite the same for me so I'll have to check this out.

Warzone 2100 is an RTS from 1999 that went open source at some point and can be played on just about anything. It's unit design functionality is really cool and I'm a sucker for post-apocalyptic worlds.

Unciv civilization 5 replica
Edit: added description

Here's a good start.
Fillets-ng (sokoban puzzler)
Simon Tatham’s Portable Puzzle Collection (sgt-puzzles)
Sauerbraten (FPS)
0 A.D. (RTS)
Holotz Castle (platformer)
Xmoto (motorbike trials riding)
Kobodeluxe (shmup)
Neverputt (minigolf)

Dungeon Crawl Stone Soup Love this traditional roguelike!

I really enjoy Thrive, it's basically a modern and more scientifically accurate Spore!
- Ooh, neat! Thanks for the recommendation!

I haven't seen any incremental games get posted. They aren't exactly traditional games, but so many of them are open source like Antimatter Dimensions or Synergism. Bitburner is a unique one as an incremental hacking sim, since it relies on actual scripting to grow and automate tasks.

Supertuxkart

Oh I am saving this post! It's a goldmine

Tux Racer. Hands down.

Classic roguelikes have the most longetivity for me. Crawl, Brogue, Nethack.
- ADOM was always my favourite, but Dungeon Crawl: Stone Soup is my go-to these days.
  Shattered Pixel Dungeon on android is also fantastic and has wonderful touch screen controls.
- This. I just keep coming back to nethack.

Oof, I have a huge boner for roguelikes, and most of them are open source. My biggest time sink is still Dungeon Crawl Stone Soup, playable online at https://crawl.develz.org/

Dungeon Crawl Stone Soup

Doom :)

OpenRA has open source slightly modernized versions of Red Alert, Tiberian Dawn and Dune 2000. There's also Tiberian Sun-like and Red Alert 2 mods for it :)
- I haven't been involved in the project for a decade or so but I was one of the founders of OpenRA, so thanks for recommending it! I'm very happy it's still actively developed nearly two decades later.
- I came here to post about OpenRA too. Great game, real nostalgia hit for the days of dial up matches against a friend on Dune 2000 and Red Alert

Several, but my number one fav so far is Battle for Wesnoth. An old school hex tile turn based strategy game. Like something out of the 90's or very early 2000's.
Great art, awesome music, solid gameplay, and runs on a potato.
My best friend and I play it whenever we want a casual chill, play n' chat gaming session.
It runs great on the Steam Deck too with a few interface tweaks.
- Battle For Wesnoth is such a nostalgia hit. Great game too.
  
  Totally!
- It is from the 2000s. Its first release was in 2005.
  
  I feel old now, thanks (:
- I've installed wesnoth on at least 10 different computers and laptops over the years. My son's enjoying it now, what a classic

Pixel Dungeon! Great rogue like mobile game

Unciv! Remake of civV for desktop and Android.

Cataclysm: Dark Days Ahead

Xonotic is a fun quake-like shooter. Highly recommend.

Endgame: Singularity is a fun (and sometimes very frustrating) small strategy game worth checking out.
The Dark Mod is basically Thief but really well done with a solid amount of (fan) missions to choose from. Speaking of I should play some of it again.

Veloren

Shapez is a fairly relaxing factory game. Pretty minimalistic style but easy to lose tons of time to if you aren't careful.
- Don't think that's an open source game bud
  
  Sure it is, in fact running it yourself is one of the ways to unlock the full game content.

0 A.D. is the closest experience to Empire Earth I've had on the FOSS side. Great fun!
- Hum more Age of Empire than Empire Earth I think

Battle for Wesnoth is a personal favorite of mine that I haven't seen mentioned elsewhere in the thread. It's a pixel art, hex-grid turn based strategy game with fantasy armies. It's mixed with mild RPG elements, and there's tons and tons of campaigns and fanmade content accessible directly through a mod browser in game.
The other games I enjoy that I see being mentioned here are in the same vein. BAR, Warzone 2100, OpenTTD. And the open mods based on the STALKER engine, like Anomaly. I love those.

If reverse-engineered Nintendo games count, then Super Mario 64 and Pokemon Emerald whose engine is technically open source.
EDIT: Minecraft Beta 1.7.3 has been reverse engineered multiple times too.
- I was going to recommend Ship of Harkinian as a reverse engineered Ocarina of Time but they don't have a license file posted in their git repo so not technically open source unless I'm just missing it. It uses libultraship which is mit licensed.
  Edit: Looks like they started by forking another unlicensed project so until that project chooses a license they don't want to choose a license for themselves. What a mess.
- Reverse engineered N64 games? Can you provide a link?
  
  This GitHub should have a few. https://github.com/n64decomp/sm64
  
  https://github.com/n64decomp/sm64/blob/
  
  Since people already gave you SM64, here's Ocarina of Time. Literally the best way to play the game.

Some great games already on here, but wanted to share some love for VVVVVV which released its source a few years ago.
- What!? That's open source now!? I loved that game when I got it in a Humble Bundle. Well, time for a replay.

OpenTTD is my drug. I'm addicted
- Now see ive tried that game and it didn't quite stick it's claws into me. What about it is addicting to you?

Puzzle
Rocks'n'Diamonds - Digging for diamonds while avoiding boulders and enemies
Enigma | github - Marble puzzles (and much more) inspired by the classic game Oxyd
GNU Robbo - Solve rooms (puzzles) with your robot
Space
Oolite | github - an open-world space opera (inspired by classic game Elite)
Kobo Deluxe - 2D scrolling space shooter, destroy star bases with your ship
Open Tyrian - Arcade-style vertical scrolling shooter
- Open Tyrian is great, the original is always free on GOG Tyrian 2000

OpenRCT2, eDuke32, the various Doom and Quake games
Also ScummVM is open source and supports many games
- Yo I wasn't expecting to randomly see you here, great work on the Deus Ex randomizer!
  
  Thanks! Yeah I'm really loving Lemmy so far, btw we do have a Deus Ex community
  https://lemmy.ml/c/deus_ex
  (Unfortunately lemmy.ml has been pretty unstable, might have to wait for it to come back before you can subscribe)

I like supertuxkart and minetest
- Seconding Minetest. It's a lot of fun just to poke around the forums and work on my own little projects and additions with minimal actual programming skill required

There's not a whole lot of activity around it these days, but Zelda Classic is an engine for Zelda 1 with a number of additions and improvements, that allows for custom maps, tilesets, scripts, items, enemies, etc. etc.
I've whiled away an unreasonable amount of time on quests that are on par mechanically and quality-wise with Link's Awakening and the Oracle games. Shame I can't get the tarball to work properly on Steam Deck, it's a great fit for that hardware.

Warzone 2100. It reminds me of the older Command & Conquer games with a ton of upgrades and customization for your units.

If you didn't already suggest it, I would have suggested Veloren!
- Yep, what's promising about Veloren is I feel like everyone had a pretty cohesive idea of what Cube World was "going to be". It's pretty hard to disappoint a community when the developers are the community.

OpenTTD is a great open source clone of the transport tycoon game. And boohu is an awesome ASCII coffeebreak roguelike.

Simutrans. It's old but really good. It's really easy to lose 10h or so in it before you notice the time.
- I remember playing this with a friend. We modified the source code to allow us to use the fast-forward functionality in an online mutiplayer game. Once we figured out how to make proper grade-separated junctions, it ended up becoming quite a tedium. I wish Transport Fever had a multiplayer mode.
- Reminds me of OpenTTD. I love the classics

Teeworlds. There are some great community made modes for it like FNG and DDrace. Be sure to download it from ddnet.tw to access to extra features created by the community.
- I didn't know DDrace was open source, that's cool. It's a really cool game highly recommend it!

InfraArcana was a little bit tough but is a very good roguelike
- How does it compare to something like Brogue?
  
  I haven't played Brogue but in nutshell IA is a proper roguelike and somehow manages to create the atmosphere of being alone in the dark in a mansion full of acolytes and worse