Hi Peter,
BG is open source: I posted a link to the source below, and after
posting I saw a document about build instructions etc. It's all
JavaScript by the look of it, with some XML for window layout (I'm
guessing there, but I see a reference to "XULrunner").
The BG Download page has a link to the instructions on how to download &
build the app.
Regards,
Glen Starrett