Haven't seen these two so thought I'd add them to the list. Minetest is a block building game engine (like minecraft) built around the idea mods add all content. There are a bunch of games built for it, and last I checked a active modding community. https://www.minetest.net/ The other is AlephOne, a engine to play all the Marathon games (story FPS, pre-halo bungie made games) along with a bunch more community created…
Minetest is kinda crap, honestly. Unless it has radically changed since I played it, the game feel is just lightyears behind. It has lots of mods and customization hooks, way more than Minecraft, and if that works for you that's great. But for a lot of people the experience just can't compare.
there is a minecraft mod in minetest: https://content.minetest.net/packages/Wuzzy/mineclone2/