"qooxdoo-contrib" is an infrastructure for users to share qooxdoo related code with others.
Contributions come in many different forms: the typical widgets, but also custom backends, themes or qooxdoo classes to complement or enhance the framework.
It provides a consistent infrastructure to allow contributors to develop and release their work independent of the state and progress of the qooxdoo core framework.
Check out the contrib catalog website, which makes finding a suitable contrib easy.
The contrib manual page explains in detail how to use contributions as well as what to bear in mind when writing your own contribution.
Use the regular qooxdoo-devel mailing list for support and tech discussions about contributions.