It's a general purpose dual bipolar timer IC. The NE556N combines two 555 Timer IC's in one 14 pin DIL package.
Difference Between 555 and 556 IC: The NE556 is the successor of the classic 555 Timer IC. It has two Timers inside a single package. This reduces the form factor and complexity of the system. Functionality and pin description wise both 555 and 556 are identical.