This team is currently compiling the help screens for Joomla 1.6. These are being served from this wiki and you can see a summary page showing the current status of each page here. For further information see the call for help announcement.
The aim of the API Reference Project is to construct a useful reference manual on the Joomla 1.5 (and later) Framework API which will complement, rather than replace, the automatically generated material on http://api.joomla.org. The starting point for the API Reference is the Framework page which lists all of the classes in the Framework API.