CSOUND is a powerful tool for computerized sound generation. CSOUND takes two input files -- an orchestra file and a score file. In the orchestra file, you define what your instruments are, what they sound like, what kind of waveforms they should use. In the score file, you define when and how to play those instruments. CSOUND gives the programmer/user/musician extreme power over the control of the sound they generate -- anything from extremely simple beeps to fully textured sounds that emulate many real instruments.
For more detail, see my notes on CSOUND.