You want to use a Serial Monitor better than the one included in Mac OS or in your MCU (Arduino, Teensy, Raspberry, Beaglebone) development environment? You want to be able to send and receive messages? You want to log debug messages or any kind of text? You want to follow the value of variables? You want to plot variables, functions, curves? You even want to draw geometrical shapes?
Then Extended Serial Monitor is what you need. Extended Serial Monitor allows you to extend the capacities of your Arduino or Raspberry default Serial Monitor.