Qt is a cross-platform graphical widget toolkit for the development of GUI programs. Qt is most notably used in the K Desktop Environment (KDE).
Qt uses an extended version of the C++ programming language, but bindings exist for Python, Ruby, C, Perl and Pascal. It runs on all major platforms, and has extensive internationalization support. Non-GUI features include SQL database access, XML parsing, thread management, and a unified cross-platform API for file handling.
Qt has nothing to do with Apple's Quicktime.