Hi devs!
I have finally made it to publish some code documentation which was created using the phpDoc from the source files: http://roundcube.net/doc/phpdoc/
There's also a wiki page describing the directory structure and some important functions: http://trac.roundcube.net/trac.cgi/wiki/Dev_Docs
Hope this will help you guys to get familiar with the RoundCube code base. I'll try to continue describing how RC works. Please let me know, if you miss any kind of information. For me, everything seems to be clear :-)
~Thomas
List info: http://lists.roundcube.net/dev/