You can write markdown with added benefits of React components and this Gatsby starter will render a GitBook theme documentation site. Self host using Docker or build the static bundle and deploy to Netlify :)
Disclaimer: I maintain this starter.
The open source repo still exists but it’s abandoned.
I wish they could have found a path to money without destroying their open source offering.
Docsify needs maintainers btw. It's a worthwhile project! https://github.com/docsifyjs/docsify
When gitbook moved (rather poorly - there was a lot of confusion on what would happen to the old codebase) to a service, mdbook is what I switched over to, and I'm glad I had been forced to look for an alternative to gitbook.
Haven't really done anything with Rust, but having been bitten once, my research suggested they'd be unlikely to drop mdbook anytime soon.
Edit: example GitLab-hosted book: https://gitlab.com/strivinglife/book-git-commands
One of the main things I like about static site generators is that they are so simple to host.
-Brian