The NE555 is a precision timer IC capable of producing accurate time delays or oscillation. In the time-delay or monostable mode of operation, the timed interval is controlled by a single external resistor and capacitor network. In the astable mode of operation, the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor.

NE556 is a dual timer chip, means it has two 555 timer circuit in 14 Pin DIP package.

LM556 is a dual timer chip, means it has two 555 timer circuit in 14 Pin DIP package.