MuseScore is a free musical notation program for OS X, Windows and Gnu/Linux. Created by Werner Schweer, it is released as free and open-source software under the GNU General Public License.
It is a complete scorewriter and notation editor with a feature set comparable to Sibelius or Finale, and supports a wide variety of file formats and input methods.
For my first attempt at MuseScore Plugin Development, I present a simple game of musical dice or Musikalisches Würfelspiel made with qt and JavaScript. Generate a waltz by throwing 2 six sided die and inputting the results into the dialog box in MuseScore to generate a unique melody. The total unique pieces this generates is over a quadrillion (granted they will sound quite similar).
Here is the code.
Examples:
(rolled for key and transposed it using the gui)
