How can I download this app?
If you're referring to the A2 SketchUp plugin, here's a link: Download A2 SketchUp
I do not recommend this as it bundles and redistributes other authors plugins.
This person / company ("dem" at SCF) was told to get distribution permission from all plugin authors, did they ?http://sketchucation.com/forums/viewtopic.php?f=323&t=61729
And it has not been updated since 2015.
I didn't dig deeper on this, my apologies.