Shorten
Shorten is one of the oldest Lossless audio formats. It was created by Tony Robinson in the mid-nineties.
It lacks several features like seekability (although there is a "hack" that adds seek support), streamability, support for Multichannel and high sampling rates, tagging, ...
The reason why it became very popular is that it was the first open source lossless compressor. It gained huge momentum years ago because of this.
Addtional Reading
Extra-official Shorten website at etree- Lossless Codec Comparison by Rjamorim