ATRAC: Adaptive Transform Acoustic Coding for MiniDisc - ATRAC is an audio format based on psychoacoustic principles originally used for Sony MiniDisc players.
Free Lossless Audio Coder - FLAC is an open source lossless audio codec, supports streaming, seeking and archival.
GSM 06.10 Lossy Speech Compression Format - Details about the format and example source code.
Lossless compression vs. speed - Comparisons of most popular lossless audio formats.
MPE Secure Media - Secure streaming media format giving authors, songwriters and publishers complete control over products distributed through the internet.
Musepack - Open audio compression format also known as MPC or MPEGPlus/MP+. Based on MPEG1 Layer-2/MP2 algorithms.