The Documentation Working Group currently maintains the following websites:
This entire site is automatically generated by the phpDocumentor package from an analysis of the Joomla! source code and making use of specially formatted comments embedded in the source code itself. It is an invaluable tool for all Joomla! developers.
The concept behind docs.joomla.org is that it will become the central resource for developing single-source modular documentation within the Joomla! project. The idea is that we write stuff once then re-use it in a somewhat analogous way to modern OOP software development. In the future we expect that other sites, such as help.joomla.org and developer.joomla.org will contain some, or even most, of their content derived from sources here. By building a central database of document "chunks" we gain maximum benefit from the efforts of a limited number of authors and we produce "agile" documents where a single change is rapidly propagated to all the derived documents affected.
Those interested in the techniques will find more information here.
The official help site houses much of our early documentation, including that for Joomla! 1.0.x, the help screens for all Joomla! versions and the Joomla! 1.5 Installation Guide.