Qt development files (Threaded) Qt is a C++ class library optimized for graphical user interface development. This package contains the libqt-mt.so symlink, necessary for building threaded Qt applications as well as the libqui.so symlink and the necessary header files for libqui.so. (See README.Debian and the Qt Documentation for instructions on libqui.so) WARNING: If you plan to build some older Qt3 applications, you will most probably have to install the libqt3-compat-headers package. It contains all the headers which are not part of the official Qt3 API anymore but which are still used by some programs. So if you encounter problems with missing header files, please install this package first before you send a bugreport.