This library provides a simple on-target debugger for AVR based Arduino boards. Debug commands are added to the sketch and a debug shell is called on break-points, assert, etc. Below is a screen-shot from the demo sketch run on an Arduino Mega2560 with Arduino IDE 1.6.7.
Please find more details in the README file.
Cheers!
NB: When running the demo sketch please enable "Display line numbers" in Arduino IDE Preferences and run the Serial Monitor with "Newline".