Other GUI Toolkits
Currently there are two main widget toolkits in the Amiga world, and are competing each other. The most widely used is MUI (adopted into AROS, MorphOS and in most Amiga programs), the other one is ReAction which was adopted in AmigaOS 3.5. There is in development a GTK MUI wrapper and it will allow the porting of various GTK based software. There is also modern interfaces based on XML, Feelin.
Read more about this topic: Magic User Interface