Project Zomboid is a blast, especially when you really dig into the options for changing game rules. You can basically craft your own custom zombie apocalypse. You can decide how the virus works, whether zombies are slow or fast, whether they have good eyesight, good hearing, how strong they are, where they spawn. You can change loot rarities, how long it’s been since the outbreak started, when the power gets shut off, etc, etc.

Factorio

UT2004

Vintage Story with mods. Vintage Story is a minecraft-like wilderness survivor game focusing on long term survival, not just “eat berries”. it’s under active development. https://mods.vintagestory.at/vsds the server docker image if interested.

https://linuxgsm.com/servers/

Palworld and Terraria, particularly with Tmodloader, are fun options.

Final Fantasy XI is still a beautiful game and is self hostable, but as with most MMORPGs, you need lots of people to get the full experience. Luckily if you’re hosting your own, you can always mod settings to make yourself lvl 99, turn off enemy AI, teleport anywhere, or whatever.

To add my own two cents into this mix.

RuneScape classic with the fan made OepnRSC

And Final Fantasy XI … kiinnddaa. Not sure if that one’s feature complete yet or ever will be. But there’s a fan server effort for it like RuneScape.

Veloren has been a blast on my family’s self hosted system.

I ran a 7 days to die server for a few years, fun to do missions with a lot of friends, and build bases and stuff.

We’ve spent last few months playing Enshrouded. The dedicated server is a resource hog tho, even on an empty server it’d use a ton of CPU time. Still lots of fun with a few friends exploring and building stuff

I ran a fairly popular RTCW server back in the day… Insta-gib and sniper rifles only. Good times.

Mindustry

Starseige tribes? Trackmania?