Writing Client Applications for Fedora
Until we update this page, one of the better references on this topic is Matt Zumwalt's post outlining Inroads to Application Development for Fedora Commons on the MediaShelf Blog.
Frameworks known to be used with Fedora
Spring (with Struts), Drupal, Ruby (Rails/Merb), Plone, Pylons
For a more complete listing of publicly available client applications used with Fedora, visit the Fedora Tools page