Synthesizer

Traditionally, a synthesizer is considered an electronic instrument that produces (or generates signals that help other computer parts produce) sound via speaker or other audio output. So it's basically a piece of hardware that puts out some 0s and 1s and the speaker handles the rest.

Historical Examples of Synthesizers
There were plenty of predecessors to the above definition of a synthesizer, such as those involving electric generators, vaccuum tubes, optoelectronics, etc. But in formal definitions, the Hammond Novachord was considered to be the first polyphonic synthesizer to make it to the market. Other examples include: Up until we started getting digital synthesizers, most synths (analog synthesizers) relied on special inner materials of unique types to create a particular sound, and these would be modified with dials and such. With the introduction of digital synthesizers, the entire production of the synth would be on the circuit board. Eventually we got what are termed as softsynths, which are applications run on an operating system that work as a synth, often connecting to a digital audio workstation, a MIDI controller, or the keyboard itself for interaction.
 * Solovox (Hammond Organ Company)
 * Multimonica (Hohner and Harald Bode)
 * Electronic Sackbut (Hugh Le Caine)
 * Magna Organ (Yamaha)
 * Moog (Robert Moog and Wendy Carlos)
 * Buchla Modular Electronic Music System (Don Buchla)
 * EP-30 (Roland Corporation)
 * GX-1 (Yamaha)
 * DX7 Digital Synthesizer (Yamaha)