Jack

JACK is a low-latency audio server, written for POSIX compliant operating systems such as Linux and Apple's OS X. It can connect a number of different applications to an audio device, as well as allowing them to share audio between themselves. Its clients can run in their own processes (ie. as normal applications), or can they can run within the JACK server (ie. as a "plugin").

JACK was designed from the ground up for professional audio work, and its design focuses on two key areas: synchronous execution of all clients, and low latency operation.

Applications using jack
For a long (official) list of applications that (can) use jack see here

Control & configuration

 * qjackctl

Audio players

 * AlsaPlayer
 * xmms-jack -- Jack plugin for XMMS

Audio editors

 * Ardour

MIDI editors

 * Rosegarden

Software Synthesizers

 * FluidSynth
 * Timidity (only in recent versions from CVS)

Misc.

 * GStreamer