PortAudio is a free, cross-platform, open-source, audio I/O library.
It lets you write simple audio programs in 'C' or C++ that will compile and run
on many platforms including Windows, Macintosh OS X, and Unix (OSS/ALSA).
It is intended to promote the exchange of audio software between developers
on different platforms. Many applications use PortAudio for Audio I/O.

PortAudio provides a very simple API for recording and/or playing sound using
a simple callback function or a blocking read/write interface.
Example programs are included that play sine waves, process audio input
(guitar fuzz), record and playback audio, list available audio devices, etc.