Knubbi:

In Preferences you can (de-)activate Magnetism . When activated, all corners and rotation are done in 15 degree increments. This makes it fairly easy to make 90 degree corners.

I can think of a few hundred ways to make SH3D better or more powerful, but the main strength of this program is its ease of use. Everybody can use this program within minutes, because of its intuitive user interface. I've been using the program for six months now, and there have been numerous improvements during that time, and I'm sure many more will follow.

Hans