SoftSynth.com
Music and synthesis software API, including JSyn and JavaSonics ListenUp.

Zerius Development Inc.
Java program for designing and generating sounds on-line. Also a vocoder for download.

Deepsound
JavaScript sample calculators, time-stretch, pitch-shifting, sample length, delays, sampling rates, and durations.

JavaZoom
Java MP3 Player supports WAV, AU, AIFF, Ogg Vorbis also.

JavaTuner
Tunings and temperaments. Demo applet.

FreeMusicPlayer
Part Java part native, supports MP3, WAV, Ogg, and playlists. Windows 2000/XP.

jOggPlayer
Gui Enhanced Vorbis Ogg Player. Freeware.

FreeTTS Speech Synthesizer
Written in Java, based upon Flite 1.1: a run-time speech synthesis engine from Carnegie Mellon. Open source, BSD.

Java Jukebox
Copy and paste html code to add a jukebox to your web site. Digital clock and page jump also.

Xenoage MusicXML Player
Applet and standalone application that plays MusicXML files and converts them into MIDI format.

MuSing
Aids the creation of musical rhythms.

Neuralsemantics Modulator Jane
Applet uses standard AU sound files to modulate graphics on web page. Also offers Neurosonic e-Guitar.

Sonicle Audio
WebSynth product line. Applets, players. Some freeware.

JFugue
API for specifying music using simple strings and easily transforming patterns of music.

RPitch
Relative pitch ear training to recognize intervals. Freeware.