We have good experiences with DocBook for the manual. From the XML source files we can create the manual in many formats like HTML and CHM.
Maybe we can give Publican a try. Publican is a publication system, which use DocBook as file format and is optimized for translation.
We should use this wiki as developer documentation.
For the offline use you can clone the text sources and maybe we can write with creoleparser a python script to convert the wiki files to HTML files.
We use Doxygen for documenting the code.