Multivibrator

Wikipedia:

A multivibrator is an electronic circuit used to implement a variety of simple two-state systems such as oscillators, timers and flip-flops. It is characterized by two amplifying devices (transistors, electron tubes or other devices) cross-coupled by resistors and capacitors. The most common form is the astable or oscillating type, which generates a square wave—the high level of harmonics in its output is what gives the multivibrator its common name.

http://en.wikipedia.org/wiki/Multivibrator Can be used to build oscillators, touch switches, flip flops and so on.