The Doctave CLI is more like MkDocs or Docusaurus in that it supports a docs-as-code workflow. It takes your Markdown files and generates a pretty documentation site from them. It's more batteries-included and opinionated though: it has limited customizability by design, so that you don't have to wrestle with plugins or spend time bikeshedding themes. You just install Doctave (a static binary), write your docs, and host the site on e.g. GitHub Pages.
For an example site, the docs for Doctave can be found at https://cli.doctave.com
There is also https://www.doctave.com which is a dedicated host for Doctave documentation sites. It's aimed at teams that want to do docs-as-code, but still want to have all their docs centralized and searchable under one roof. This is closer to GitBook.com, but Doctave still uses a docs-as-code approach instead of GitBook, which is mostly used through a WYSIWYG editor and is closer to a traditional knowledge base system.
[Edit: formatting]