DokuWiki is a standards-compliant, simple-to-use Wiki mainly aimed at creating documentation of any kind. It is targeted at developer teams, workgroups, and small companies. It has a simple but powerful syntax which makes sure the datafiles remain readable outside the Wiki, and eases the creation of structured texts. All data is stored in plain text files, so no database is needed
GNU TeXmacs is a free wysiwyw (what you see is what you want) editing platform with special features for scientists. The software aims to provide a unified and user friendly framework for editing structured documents with different types of content: text, mathematics, graphics, interactive content. TeXmacs can also be used as an interface to many external systems for computer algebra, numerical analysis, and statistics. New presentation styles can be written by the user and new features can be added to the editor using Scheme.
DocBook is an XML vocabulary which enables you to create document content in a presentation-neutral form that captures the logical structure of the content. Using the DocBook Project XSL stylesheets, you can publish DocBook content as HTML pages and PDF files and other formats, including man pages, HTML Help, and JavaHelp.
gjots lets you organize text notes in a convenient, hierarchical way. It can be used for notes, jottings, bits and pieces, recipes, and even PINs and passwords, using encryption. It can also be used to "mind-map" larger compositions like manuals, Web pages, articles, etc. It is a bit like the KDE program "kjots", but uses the GTK library and supports a hierarchy of folders. Files can be output to HTML with an automatic table of contents or to docbook XML. Encryption is supported with ccrypt(1), gpg(1), and openssl(1), so that musings can be kept private.
tex-upmethodology provides a complete set of LaTeX styles that permit you to write documents according to a UP-based methodology. Its major features are document history, task management, design and specification documentation, and helping tools. tex-upmethodology is officially supported by CTAN.
DocBook Doclet creates DocBook XML and class diagrams from Javadoc comments, converts HTML to DocBook, and transfoms DocBook XML into various output formats. It consists of a complete DocBook distribution containing schemas and the DocBook XSL stylesheets. It also integrates Apache FOP as the XSL:FO processor. A Swing application is used to customize the doclet and most of the DocBook XSL parameters and to start the transformations.
LyX is a document processor that encourages an approach to writing based on the structure of your documents, not their appearance. It is intended for people people who write and want their writing to look great without tinkering with formatting details, font attributes, or page boundaries. On screen, it looks like any word processor, but it uses the TeX engine for printed output and producing richly cross-referenced PDFs. It is stable and fully featured.