teensy
The app communicates with your Teensy board when the HalfKay bootloader is on
The Teensy Loader program communicates with your Teensy board when the HalfKay bootloader is running, so you can download new programs and run them.
Teensy Loader always reads the latest version of your HEX file, so you can just compile your code, then press the pushbutton to program and run your code.