JACK :JACK Audio Connection Kit, is what this article is about.

JACK is a Open Source Project, and they say it best.

Have you ever wanted to take the audio output of one piece of software and send it to another? How about taking the output of that same program and send it to two others, then record the result in the first program? Or maybe you’re a programmerwho writes real-time audio and music applications and who is looking for a cross-platform API that enables not only device sharing but also inter-application audio routing, and is incredibly easy to learn and use? If so, JACK may be what you’ve been looking for.

In my particular case I am using this and many other Open Source tools to take full advantage of the technology I have around me.

JACK’s source code is available and is available on Windows, Linux and OS X.