The open-source Roblox & UEFN alternative giving you freedom to own. An all-in-one, real-time game development platform.

They just joined the Fediverse as well at:

https://mastodon.gamedev.place/@themirrorgdp

I’ve never played Roblox or Fortnite so I have no reference there. But The Mirror, while still Alpha, was lots of fun to try out and works just fine on Linux out of the box for me on Debian using the Itch Flatpak.