It's C++, and basically what Arduino gives you is

  int main() {
    setup();
    for(;;) loop();
  }

As well as a GUI to easily flash devices and view the output from the serial port, as well as import libraries that do all of the hard work like say making a serial port on any microcontroller pin or control external devices like light strips or displays.

I'd assume the average user on HN should be able to figure it out pretty easily.