Meridian Lossless Packing
It's a completely closed format - there is no source code or format documentation available. Also, the encoder is quite expensive (US$ 2500 as of October 2005).
Compression efficiency is quite bad for CD content (16 bit, 44100 Hz, stereo), being outperformed by Shorten and even RAR. It is somewhat better for high resolution content (multichannel, 24 bit, 96 kHz), but still beaten by, e.g., WavPack -h in both speed and compression. Compression is very slow.