The Guido Engine Library is a generic, portable library and API for the
graphical rendering of musical scores. The library is based on the GUIDO
Music Notation Format as the underlying data format. It takes account of
the conventional music notation system and should be flexible enough to
include any graphical sign and musical information if necessary.

The GUIDO Music Notation Format [GMN] is a formal language for score level
music representation. It is a plain-text, i.e. readable and platform
independent format capable of representing all information contained in
conventional musical scores. The basic GUIDO Format is very flexible and can
be easily extended and adapted to capture a wide variety of musical features
beyond conventional musical notation (CMN). The GUIDO design is strongly
influenced by the objective to facilitate an adequate representation of musical
material, from tiny motives up to complex symphonic scores. GUIDO is a general
purpose musical notation format; the intended range of application includes
notation software, compositional and analytical systems and tools, performance
systems, and large musical databases.  It is powerful, flexible, easily
portable, and human readable.

WWW: http://guidolib.sourceforge.net/