Mpadec is a high-quality portable MPEGaudiodecoder library. It supports MPEG-1, MPEG-2 Layer I, Layer II and Layer III audio streams, including free-format streams.
MAD is a high-quality fixed-point MPEGaudiodecoder with 24-bit output. The implementation is entirely new, based on the ISO/IEC standards, and performs especially well on systems without native floating-point support.
The goal of the Decals project was to create an open source MPEG-4 ALS audiodecoder licensed under the LGPL. That is not necessary now that there is an LGPL ALS decoder in FFmpeg. Yay!