It is a music notation application that allows you to compose and play songs.
CelticPipes is an easy-to-use music notation application (for Mac and Windows) that allows you to compose and play quality scores principally for the Great Highland Bagpipe and for the traditional 'Celtic' musical instruments like: Great Highland Bagpipe & Practice Chanter, Scottish Smallpipes, Tin Whistle (or Penny Whistle), Flute, Scottish Side (snare), Tenor & Bass drums, Bodhran.
Probably the most useful bagpipe software I have as it bridges BMW, PiobMaster and ABC compilers with ease, both for import and export. Its own interface is pleasant on the eye too. I use Lilypond for most of my own writing as it gives me excellent flexibility in compiling. However, so much is written in BMW and ABC, with a little open-source stuff in Piobmaster too, that CelticPipes is essential to me, and I use it often. Highly recommended.