Written, and released into the public domain by Josh Whelchel (@soundofjw)[http://www.twitter.com/soundofjw]
WSF is a format designed to reduce redundancy in modules. In a collection of modules that uses the same samples (game soundtracks), a lot of data for these samples will be contained twice. Obviously, this is not ideal.
WSF stores samples in a separate sample pack container (the WSP) - any duplicate samples (including samples derived from others) will dupe-checked and stored appropriately.
A side benefit: WSF also allows music to be protected using a very primitive password-encoding scheme, to encourage those who enjoy music to seek it through more appropriate channels.
WSF has been used in Konjak's Noitu Love 2, The Spirit Engine 2, Kyle Pulver's Bonesaw: The Game, and several other products.