ABC, developed by Chris Walshaw, is a format designed to notate music using plain text. It was originally designed for folk tunes of Western European origin which can be written on one staff, but has since been extended to support the notation of complete, classical music scores.
Since its introduction at the end of 1991, ABC has become very popular. Programs on many operating systems use ABC as an input and/or output format. There are programs which produce printed sheet music or allow for computer performances, search in tune databases, or that analyze tunes in some way.
The aim of this project is to promote the ABC language by maintaining the ABC standard and a set of software and source code that manipulate and present music written in ABC.
abcnotation.com
abc.sourceforge.net
ABC Tune Search
The abc tune search / tune finder gives you access to thousands of folk & traditional tunes from across the web.
Classical music extensions:
abcplus.sourceforge.net
sourceforge.net/projects/abcplus
ABC to HTML ~ sourceforge.net/projects/netabc
User Interfaces ~ sourceforge.net/projects/runabc
Reference: en.wikipedia.org/wiki/ABC_notation
The Audio File 