documentr is a Web-based tool for editing and presenting software documentation. It allows you to easily maintain documentation for multiple products and product branches. Edits can easily be copied between branches, with merge conflicts being handled gracefully. It uses Markdown as its markup language, along with some extensions, and has a role-based permission system.
The DocBook Authoring and Publishing Suite (DAPS) provides a tool set for easy creation and publication of DocBook sources on Linux. It lets you create HTML (including Webhelp), PDF, EPUB, man pages, and other formats with a single command. It automatically takes care of validating and filtering (profiling) your sources and automatically converts images into a format best suited for the output format. You can easily create profiled source tarballs for translation or review. DAPS supports authors by providing linkchecker, validator, spellchecker, and editor macros. It is well suited to manage large documentation projects with multiple authors using the DAPS docmanager.
zpub is a server to collaboratively work on DocBook-based documentation. Editors modify the XML sources with their preferred editor and submit their changes via Subversion. zpub renders the files centrally to various output formats, optionally notifies other editors, provides an archive of all previous revisions of the document, and supports a simple sign-off workflow. The documentation and user interface is currently only available in German.
QuHelp is a command-line program that scans a directory with HTML formatted text files and builds a help site using that directory's content and a template. A default template is included, but any template can be specified. QuHelp adds a nice expandable tree view of the help site's contents, a navigator, permalinks, and other useful stuff for browsing the help site.
Aephea is a text-based authoring tool for HTML. It enforces well-formedness with a simpler and stricter TeX-like syntax and provides useful extensions and abstractions with facilities for adding new ones. It emphasizes a single unified approach that stays close to HTML itself and promotes and utilizes CSS extensively. Abstractions such as dictionary stacks, arithmetic, and iteration are part of Aephea.
BullDoc is a Web application for documentation building. It is generally desgined for projects developed with PHP and which use SVN or another source control system. It stores the documentation sources in the same repository as the code. The sources should be text files, so SVN can track changes and allow BullDoc to always extract a documentation version appropriate to the code. It makes it convenient to view the result of authoring by opening a page in a Web browser, without additional compiling. It also allows you to edit text directly in the Web browser.