Qarbon has silently dropped the Mac version of Viewletbuilder software. Related: Screencasting on a Mac
Qarbon released ViewletBuilder for the Mac in May 2005 but this month, Qarbon removed the Mac edition from both the Qarbon trial dowload page and Online Store.
The Viewletbuilder Features page still talks of Viewletbuilder support for Windows, Mac, and Linux.
Download Mac Viewletbuilder 4 datasheet [pdf]
Update: We have received no official comment on Mac Viewletbuilder from Qarbon.