This ABC to notation converter was developed by Michael Eskin.
Full project source may be found on: GitHub.
Try it out here: ABC Transcription Tools.
The following sites are great starting locations for finding tunes in ABC format:
The Session - Jeremy Keith's legendary site with thousands of tunes in multiple versions.
The Reverend's ABC Tune Search - Pete Strickler's full featured tune search engine.
ABC Notation - Has a vast number of linked sites with collections of ABC files. It also has a tune search engine.
JC's ABC Tune Finder - John Chamber's comprehensive search engine for tunes.
Henrik Norbeck's ABC Tunes - A massive collection of tunes for traditional Irish and Swedish music.
The following sites are great starting locations for finding tunes in MusicXML format:
MScoreLib - Music Library in MusicXML - A huge collection of classical pieces in MusicXML format.
Music in MusicXML - Links to several large collections of music in MusicXML format.
ABC Specification
The full specification for ABC notation can be found at:
The ABC Music Standard 2.1 (Dec 2011)
ABC 2.1 Quick Reference Card
Download this handy ABC 2.1 Quick Reference Card put together by Stephen Merrony: