Gendocs is described as 'hosted documentation which tries to make it as simple as possible for you to host your documentation' and is an app. There are more than 10 alternatives to Gendocs for a variety of platforms, including Self-Hosted solutions, Linux, Online / Web-based, Mac and Windows. The best alternative is GitBook, which is free. Other great apps like Gendocs are Read The Docs, Sphinx, Docsify.js and Archivy.
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.
docsify generates your documentation website on the fly. Unlike GitBook, it does not generate static html files. Instead, it smartly loads and parses your Markdown files and displays them as website. All you need to do is create an index.
A documentation generator that builds HTML output based on Markdown files. Supports Markdown specs and offers a wide set of custom components using Markdown-like syntax. Builds Reference Source documentation for .NET projects (more added soon).
ditto inspired by flatdoc is a markdown code documentation system, capable of producing documentation similar to Three.js and Backbone.js, check out live demo here. It is designed for people who use Github Pages to host their code documentation, but you can also host it yourself.