Tilemap Town
I have an online hangout game called Tilemap Town which is kind of like a mix of old BYOND building games, MU*s, Furcadia, Pony Town, Second Life, and other things like that. It's my own attempt at establishing a space online that's not just one of the small handful of big social media sites. You can wander around on a map (or a network of connected maps!) with other people and build a house or whatever else you like, and it's intended to be a space that would be good to hang out in in-character or roleplay in. You can use your own graphics for your avatar, and use custom tile sets when building (though it's a little clunky currently).
I tried to design everything where it's easy to bring in your own graphics that don't seem out of place next to everything else, instead of having to learn 3D modeling or be really good at animation. To try to achieve that goal, it's designed around 16x16 tiles and minimal animation, with a 32x32 cap on player graphics.
Unlike a lot of other virtual worlds that are fussy about not using third party clients, I have the code all open source and I've documented the protocol too. I intentionally tried to make sure it's easy to make a client or a bot, by building the protocol around JSON (which just about any language should be able to parse) and making it so a client can ignore fields or messages it doesn't understand, so you can make something minimal that's still useful. For example, I made a 3DS client that doesn't have building but you can explore and chat! I have an alternative protocol thought up that should be easier to process for even older consoles if I ever end up with a way to get them online; I'd love to do a SNES client!
I work on it on and off, and I like to hop in and add stuff when I come up with something cool to add! Something I've been working on currently is making it so you can have arcade machines and computers and stuff in your house that you can walk up to and interact with, and laying all the foundation for that.