But I host Titanfall servers. People are able to play on them using the Northstar client, a mod for the game that lets you connect to community servers, as well as mod the game in general.
Terraria. It's a sort of hybrid between a minecraft 2d and an action RPG, really fun game with lots of content.
You can play it as standalone or as co-op and the server component is included in the game for you to host it if you want.
Tho If by interesting you mean MMOs, there are emulators for a few of them, WoW is my favorite (TrinityCore, AzerothCore), but know that opening them up to public use is illegal (copyright violation).
These are ones I keep coming back to: Farming Simulator, Satisfactory, and Valheim. I've also kept up a V-Rising server at times because my friends like it, but I'm not as into that game. Always on the lookout for games to host for friends, so I'm glad I stumbled upon this thread! Found a few in here I'm going to try out.
Garry's mod. Doesn't use a lot of resources (compared to newer games like Satisfactory), and you have an almost unlimited amount of content and things to do because of the Community Workshop.