Ask HN: Is there any advanced web-based IDE?

I don't know if this qualifies but JetBrains has an IDE that competes with VSCode called Fleet.

https://www.jetbrains.com/fleet/

Is there any web-based version of VSCode other than VSCode.dev or any open source alternative?

This maybe? https://github.com/coder/code-server

You can find some old -and open source- versions of Cloud 9. But running it is, well, not super-easy. Current versions are only available on AWS.