JSyn - modular synthesis API for Java.
JMSL - Java Music Specification Language
PortAudio - cross platform audio I/O API for 'C'

Audio Examples made using JSyn - a Java Synthesizer API

How it works:

A melody based on relative just intonation is played on a filtered sawtooth  instrument. That melody is echoed by a bell sound made using amplitude modulation.

A filtered swoop of noise, a granular cloud, and a swarm of triangle waves accompany the lead melody.

To hear sound, check the "Play" box next to the nameof the sound. Each sound uses information from either the A or B channel. You can select which channel the sound uses, and can also request random changes in a channel.