The LM555 timer (IC1) is configured as a monostable multivibrator that generates a pulse. This monostable output serves as the clock input for CD4033 (IC2). IC2 increments on every positive clock edge ...

This one comes to us by way of [Astronomermike], who chose to make a digital circuit with nothing but 555s and a largish handful of passives as his entry in the current 555 Timer Contest.