PortAudio is a free, cross platform, open-source, audio I/O library. It lets you write simple audio programs in 'C' that will compile and run on many platforms including Windows, Macintosh (8,9,X), Unix (OSS), SGI, and BeOS. PortAudio is intended to promote the exchange of audio synthesis software between developers on different platforms, and was recently selected as the audio component of a larger PortMusic project that includes MIDI and sound file support.

PortAudio provides a very simple API for recording and/or playing sound using a simple callback function. Example programs are included that synthesize sine waves and pink noise, perform fuzz distortion on a guitar, list available audio devices, etc.