I don't play videogames every day or complete a lot, but i like some simple games, and I see Minetest perfect videogame, bacause it's give me all, what i want from videogame.
Installing Minetest, you have two simple games, "Minetest Game" and "Development Test". To just build something with friends or yourself it's enough. It's have that atmosphere, that going back you to this times, when Minecraft don't have so much blocks, and you should experiment, to make something cool, and simple, like i do with my brothers, and we have fun. :)
Unlike Minecraft, Minetest have Modding API included, so you don't need to install Forge. You can download mods in-game.
Every component of Minetest, like main game, engine, and mods can be modified in game extanded settings. Every prameter have it's own name for undertanding for everyone.
you have a lot of map generators, biomes and ways to customize it. Some of them looks really unusual, like "Fractal".
Playling Minetest, you can visit some on servers, that you can found with official server list, or chnge it on another list with extanded settings. Public servers have some security issues, but you can run local server, that will work with all mods, you want.
GNU loves Minetest, and give it to you as alternative to Minecraft. Also, not only game opensource and free, it's mod's and textures. Some of them have non-free aasets, but you are being warned about it.