A free UML modelling package.
Microsoft HTML Help 1.4 SDK
A very good tool (and free) for creating html help files, i.e. chm files.
This excellent application allows you to create pdf documents simply by printing to a virtual printer.
A free reader for pdf documents.
A free reader for ps documents.
Dimitri van Heesch
A tool for documenting source code by extracting interfaces and comments directly from the code.
Open source. Convert your documents into pdf files by printing to a virtual printer.
Free open source Office suite, that is compatible with Microsoft Office.
A free, open source, utility for generating documentation from source code.
A great tool for generating graphs from simple text representations.