what does build gui app do in the ide?

This option doesn't seem to change anything. What does it do?

Shouldn't make any difference when running from the IDE, but running a non-GUI executable on its own should open up a command line window to display Print/Input statements etc. whereas a GUI one won't.

Thanks - makes a world of sense now :)

One of the many mistakes I made today in learning more about BMax was turning the option off thinking it was something to do with the GUI expansion and then wondering why - when I compiled on a Mac rather than PC - I had no keyboard control over my application...

We live and learn :).