The wiki has become the clear choice for use among projects for their help documentation. Wiki Web Help takes the wiki concept and tailors it for use specifically with help documentation. It combines the best of both worlds, with operation similar to a chm viewer and the Web technologies that enable community involvement. It features a dual split pane with tabs for searching, index browsing, and display of contents (in a tree). Users can create and modify topics and pages. Pages can be tagged for index creation. Searching with highlighting is included.
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.
Sputnik is a content management system (CMS) designed for extensibility. It works as a wiki out of the box, but can be extended into other things. It offers editable nodes, history and diff, user accounts with optional email validation, a flexible permission system, RSS feeds, and more. Sputnik supports access control and has editable templates. It can be used to maintain a personal Web site that doesn't look like a wiki and that only you can edit. Sputnik is easy to install on shared hosting without root accounts.
Synoptic is "GMail for your notes", meant to keep and categorize a large number of smallish notes and tidbits of information. Tagged overviews that retain order make it easy to maintain a good overview of your things. Adaptive tag clouds plus integration with browser bookmarks and forward/back navigation allow for easy navigation. Written in pure Python, it runs as a local Web server.
Leandoc is a small documentation generator. Unlike other generators like Doxygen or epydoc, it is designed with simplicity in mind. While the others generate dozens of files, a complex directory hierarchy, and an untold number of support files, leandoc parses the files through the command line and prints one single file to stdout.
Tartan is a text parsing engine targeted at wiki text. The syntax specification is defined in YAML in the form of regex-based rules. It supports layering and multiple output types. Rules for Markdown to HTML are included, with optional layered extensions for tables. It is implemented in Ruby, but looking to have implementations in other languages.
TEKlib is a library and operating system effort. It runs hosted on platforms such as Unix and Windows. It can serve as a freestanding operating system on architectures such as the Playstation 2. It is also a middleware that provides a constistent interface across all hosting environments. Its freestanding nature, small footprint, and absence of global data recommend it as a layer for portability and code reuse in heterogeneous environments.