GDT is about snapping building blocks together, just like those you can buy in the local toy store. Maybe you even have played with something like this when you were a kid.
GDT is a graphics editor that uses building blocks and it works very well. There are plenty of building blocks available and new ones gets added frequently, so GDT is not just a hammer. It's a whole collection of graphics tools, thus it's named GraphicDesignerToolbox and it's powerful!
GDT is targeted towards professional web designers and artists.