The best summary of available code documenting methods is

"http://en.wikipedia.org/wiki/Software_documentation":http://en.wikipedia.org/wiki/Software_documentation

which includes a "list":http://en.wikipedia.org/wiki/List_of_documentation_generators of all popular documentation generating software and a "comparison matrix":http://en.wikipedia.org/wiki/Comparison_of_documentation_generators

The following state they support fortran90

* "f90doc":http://theory.lcs.mit.edu/%7Eedemaine/f90doc/

* "ROBODoc":http://www.xs4all.nl/%7Erfsber/Robo/robodoc.html


There are also commercial products eg for fortran

"Understand for FORTRAN":http://www.scitools.com/uf.html


It is desirable to have the same source code documenting system accross all languages/modules. Doxygen & ROBODoc stand out as possible choices. This really needs a hands on experiment with these two now. 

Questions to resolve include

* Can Doxygen be made to work on Fortran90?

* Can ROBODoc work on IDL's?

* which output formats do we really want?