Mkdocs - https://www.mkdocs.org

And to make it pretty we use mkdocs material - https://squidfunk.github.io/mkdocs-material/

There's a lot of great extensions that offer more functionality and features too - https://squidfunk.github.io/mkdocs-material/extensions/admon...

There's also extensions not listed in here that you can Google if looking for something specific