Frame builders: Anyone have tubemiter.exe application?

The app isn't going to mitre the tubes for you.
A, fairly, basic drawing will tell you where to cut.
Or you could use Autocad, if you want.
Or you could write the "tiny" app for yourself

Fruitbat - I found tube-mitre extremely useful, as you can print out highly accurate cutting templates, showing both inside and outside lines. When you want your tubes to be exactly the lengths you want them, just keeping filing 'till the mitre is perfect can give under length tubes. I can only assume from your comments that you either have never tried producing multiple mitres at fixed lengths good enough to fillet braze, or you do it so often it has become second nature. I am also guessing you are probably not a software developer. Writing something like tube-mitre and getting it to print almost mm perfect aint easy.

Tube mitre can be downloaded from here:
http://www.tonyfoale.com/software.htm
5th one down.