Shorten (SHN) is a file format used for compressing audio data.
Shorten is no longer developed and other lossless audio codecs such as FLAC, Monkey's Audio (APE), TTA, and WavPack (WV) have become more popular.
It is still in use to trade concert recordings that are already encoded as Shorten files.
All libavcodec based players and converters support the Shorten codec; and since the LAVFilters are based on libavcodec, support can easily be added to Windows Media Player and other software that uses the standard filter / codec APIs.
As far as less common programs, some Rockbox applications can play Shorten files without decompression, and third-party Shorten plug-ins exist for Nero Burning ROM, Foobar2000, and Winamp; alternately VLC media player is an actually updated choice, or ffplay from the ffmpeg package if a command line utility is desired.