I use GM Toolkit.
Just as Ben said, "lots of custom programs"
I use it mostly to create 11X17 GM Standard drawings
and for Checking for DCS (Data Creation Standard) compliance.
There are a lot of tools and I only know some of them.
Don't have the time to check out the other stuff.
I did use the tank analysis. It has options to determine
at what level a certain volume of a tank would be, including vapor levels, and at different grades.