First up is Utopia: Origin!
It's an obscure survival MMO in which you get to explore a fantasy world. It's basically a survival MMO where you can do... pretty much whatever you want. There's no storyline to complete; you can just chill, harvest resources, craft what you want, explore... it's a fun little game to play.
However, the game IS a mobile game and you need a mobile emulator to play it if you use a PC (like me).
I'm pretty sure the devs of the game are okay with it, because on their website, they linked to a download of the .apk file.
.apk files can only be run on android. So I'm pretty sure... they do like it if people emulate the game on PCs.
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There's also Mini World: Creata, another obscure mobile game.
It's kind of a ripoff of Minecraft, but it's a pretty good ripoff. A ripoff decent enough that I would recommend it if you can't play Minecraft for whatever reason, along with Minetest.
They've got multiplayer, a very gorgeous artstyle, very gorgeous assets, different monsters in the survival mode, furniture, mounts (although you DO need to pay to get them), and some modding capabilities!
However, the modding capabilities aren't as good as Minecraft. You can do some basic stuff with modding... but I doubt you can do stuff like adding new dimensions. You can add items, and make models for said items, though!
For things like skins, you can either get them through paying money or through events.
Although some blocks you do need to unlock through the Garden, a feature skewed towards paying features... it's only stuff like furniture though.
Almost everything is free, and the stuff you DO need to pay for is cosmetic. Except for mounts, and the blocks. Still, I don't find the paying stuff obnoxious.
From my experience with the game, you also didn't need to get an account to play multiplayer. You just did 'guest' option (or something like that) typed in your username... and played.
You need a mobile emulator for this one as well, if you want to play it on a PC.