http://www.qtsoftware.de/oxShop/ is a cross platform frame work for user interfaces. KDE makes heavy use of it. To develop QT applications there is the qtcreator IDE that combines differed individual tools as the GUI creator that allows to draw the GUI and create the necessary code to interface to the application. Additionally many other ways and IDE's exist to support QT and also interfaces to other programming languages exist. There are some incompatibilities between the major versions of QT so Gentoo makes use of slotted package to have them installed in parallel,