Dox is a documentation browser.
It's an extensible browser for manpages and HTML documentation.
It allows you to access documentation via tables of contents, keyword indices, and full text searches.
Interfaces to pydoc and perldoc are provided. Doxygen-generated documentation can easily be integrated in the toc and index sections.
Dox comes with libc and STL documentation, and tables of contents for Perl and GNUstep.
You can easily make documentation generated by doxygen available both in the Contents and Index tabs.