Qt is a cross-platform toolkit for the development of portable programs. Contrary to popular belief, QT is about much more than user interfaces.
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. It's primary Non-GUI features include SQL database access, XML parsing, thread management, string manipulation, image processing and a unified cross-platform API for file handling.
Qt has nothing to do with Apple's Quicktime.