Things to do, eventually:

 - I know nothing about designing GUIs, and I'm afraid it shows.  Redesign.

 - Jack-keyboard does strange things to input focus and keyboard event
   handling.  Verify that it does not cause any problems.

 - Make the code cleaner.  Get rid of all these global variables etc.

 - Tooltips.

 - Fix language (english) errors in documentation and web page.

 - Add user-configurable key binding.