Wireframe-prototyping software or tool

Wireframe/prototyping software or tool

while searching for prototyping tool, came across very interesting software which have most of the design elements.
it seems like a pluginn for VISIO.

here is the link, this can be downloaded from here…

Visio – the interaction designer’s nail gun
http://www.guuui.com/issues/02_03_02.php
http://taubler.com/oversite/download.shtml