WavPack lossless audio compression. Note that, when converting .wav to this format and back again, the RIFF header is not necessarily preserved losslessly (though the audio is).
this format was originally intended for voice compression and is able to change the bit rates of encoded audio data. AMR is actively used for encoding and decoding voice while its being transmitted over network channels. The format allows one to consider network capacity and adapt it to channel loads. Due to this, the voice quality is practically undiminished.