Inqlude provides a comprehensive listing of all existing libraries for developers of applications using the Qt toolkit. Inqlude is run by the community and open for contributions.
KDE Development Platform
The KDE Development Platform provides a powerful framework for writing desktop applications and more. Among other things, the KDE libraries provide standard user interface elements, handling of configuration data, site-independent access to standard resources, network transparent input and output, embedding of application components, multimedia and hardware interaction, semantic information and tagging, advanced thread handling, and a framework for graphical desktop widgets.