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$ 2500.00 as of October/2005).
Compression efficiency is quite bad for CD content (16bit, 44100Hz, stereo), being outperformed by Shorten and even RAR. It is reportedly better for high resolution content (multichannel, 24bit, 96kHz)