For a different (and incomplete) take on a Linux Desktop in the browser permit me to plug my own project that I work on in my spare time.

https://www.youtube.com/watch?v=7namj7iy16Y

https://github.com/Lerc/notanos

This takes the approach of Still having Linux, but instead of transferring an X display to the browser, the browser supplants X. Consequently X apps don't run, but HTML/JS apps are really easy to make.

Connections are still made in a manner similar to X. A socket is available on the Unix side which apps can connect to, which tunnels through an open websocket connection.