The Mirror, [a game engine first announced the end of 2022] (https://gamefromscratch.com/the-mirror-godot-powered-commercial-game-engine/) have just made a big announcement at GDC 2024.
They are going entirely open source, releasing both their networking backend and the custom fork of Godot Engine they use as a front end, under the MIT open source license.
The Mirror aim to be an approachable development platform for games in the same vein as Roblox and UEFN, but entirely built on open source software.