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.
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.
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.
Foswiki is wiki software, supporting the editing of Web pages in an ordinary Web browser by end users. What makes Foswiki special is that it supports the embedding of active and passive macros that enhance the page content (e.g. with global or dynamic information) and allow end-users to build applications that store and process data in a structured manner.
Hatta is a small wiki engine for use inside a Mercurial repository. It can run locally and doesn't require any configuration; it's just a single Python file. It can be also configured to run on a Web server. Since the wiki can be cloned and merged along with the repository, it's perfect for working on project documentation in small teams.
Piggydb is a flexible and scalable knowledge building platform that supports a heuristic or bottom-up approach to discover new concepts or ideas based on your input. You can begin with using it as a flexible outliner, diary or notebook, and as your database grows, Piggydb helps you to shape or elaborate your own knowledge. Piggydb is a Web application provided as a self-contained package that contains a Web server and database engine.
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.
uWiki is a minimalistic wiki engine. All actions are implemented in external scripts. These scripts are wikified, and thus the wiki is extensible by itself. All dynamic access is protected through ACLs. Wiki content and Web content can be mixed in the same directory hierarchy. Markup engines and revision control are plugin-able. Currently, asciidoc as the markup engine and git as the revision control backend are provided. Subdirectories can form independent sub-wikis with own revision control. Features like distributed pages that syncronize between wikis, spam protection, and batch jobs to schedule mirroring of other content (bittorrent, git, rsync, and wget) are in planning.