What if a debugger could allow you to simply step BACKWARDS? Instead of all that hassle with guessing where to put breakpoints and the fear of typing “continue” one too many times… What if you could simply go backwards to see what went wrong?

This is the essence of the “Omniscient Debugger” — it remembers everything that happened during the run of a program, and allows the programmer to “step backwards in time” to see what happened at any point of the program. All variable values, all objects, all method calls, all exceptions are recorded and the programmer can now look at anything that happened at any time.

This video from the Google engineering lab is very good on this very subject.