FLAC is an Open Source lossless audio codec.

FLAC is comprised of
* libFLAC, a library which implements reference encoders and
  decoders, and a metadata interface
* libFLAC++, a C++ object wrapper library around libFLAC
* libOggFLAC and libOggFLAC++, which provide encoders and
  decoders for FLAC streams in an Ogg container
* flac, a command-line program for encoding and decoding files
* metaflac, a command-line program for viewing and editing FLAC
  metadata
* user and API documentation

WWW: http://flac.sourceforge.net/