Always thought the ideas behind lively kernel was interesting - web browser/js engine as the run time, webdav as the persistence layer.

https://lively-kernel.org/

Looks like they are on the third iteration now:

https://github.com/LivelyKernel/lively4-core

https://lively-kernel.org/lively4/lively4-core/start.html

Apparently now using git for persistence.