What are the main types of oscillators and their applications?

Main oscillator types include: RC oscillators (Wien bridge, phase shift) for audio frequencies with simple design; LC oscillators (Colpitts, Hartley, Clapp) for RF frequencies with good frequency stability; Crystal oscillators for high-precision frequency references in clocks and communication; and Relaxation oscillators (555 timer, astable multivibrator) for generating square waves and timing signals.