The MediaPlay Metaverse
The plan is to use the Matrix protocol as well, but right now it's still nothing. The version of Godot that this project uses might be a bit outdated, so right now it's impossible to request any web requests for now.
Why Matrix?
Metaverses definitely need to be open-source, decentralized, federated, and interoperatable with other metaverses as well, so that's why it will use Matrix for most of the federation, interoperability, you know, the stuff that make metaverses work.
Though on how it works using the Matrix protocol, it's another story, the MediaPlay metaverse is focused on building the worlds for now.
It's nice if we have some resources to set up our own Matrix homeserver, but for now it should work with a public Matrix homeserver. Just make an account and an unencrypted room and it'll work just fine. If you want end-to-end encryption (which isn't really practical for now, except for secret chats), you can use Pantalaimon.
Some people used Godot as well to make simple games with the Matrix protocol, so why not?
Mostly the desktop (Windows, macOS, GNU/Linux), but soon mobile (Android) as well.
Soon enough, though it'll be available on mobile. (if you have a VR headset for phones like Google Cardboard, VR BOX, ...)
You could try using another Matrix homeserver for now, there will be an option to use a token soon (if you're using Element, you can find it in Settings -> Help & About -> Advanced -> Access Token).
Web 3.0 will definitely come soon. Not sure if the metaverse is (really) the future of the internet or is just a hype.