Qt for AmigaOS4 has been updated and comes with huge speed improvements and bugfixes. The new release can be found on sourceforge.net and is 2 days old. Qt is used mainly for developing application software with graphical user interfaces (GUIs); however, programs without a GUI can be developed, such as command-line tools and consoles for servers. In order to actually build Qt apps, you need to fix a few issues with the native AmigaOS SDK. You can find more information in the readme file. It is highly recommended, that you use the native paint engine (default) instead of the opengl engine.