Read the Docs hosts documentation for the open source community. It supports Sphinx docs written with reStructuredText, and can pull from your Subversion, Bazaar, Git, and Mercurial repositories. The code is open source, and available on github.
MkDocs is static site generator that's geared towards building project documentation. Documentation source files are written in Markdown, and configured with a single YAML configuration file.
Daux.io is a documentation generator that uses a simple folder structure and Markdown files to create custom documentation on the fly. It helps you create great looking documentation in a developer friendly way.
Free open source software combining the best of wiki and CMS with community building-features.Discontinued
Abandoned since 2015
ReadMe is a completely customizable and collaborative place for dynamic API and/or product documentation. Users can play around with the API right in the docs, automatically generated from a Swagger / OAS file. It also works as a knowledge base platform.