An oscillator circuit that generates a signal by periodic conduction-nonconduction periods. A nonsinusoidal waveform is produced and, generally, no resonant circuits are employed.

a circuit that repeatedly alternates between two states at with a period that depends on the charging of a capacitor

a repeating circuit (like the flasher circuit

Free running circuit that outputs pulses with a period dependent or one or more RC time constants.

A circuit that uses the charge/discharge characteristics of a capacitor or inductor to produce a pulse output.

A relaxation oscillator is an oscillator in which a capacitor is charged gradually and then discharged rapidly. It's usually implemented with a resistor, a capacitor, and some sort of "threshold" device such as a neon lamp, diac, unijunction transistor, or Gunn diode.