There have apparently been alphabetically based music notation systems used informally for many years by all sorts of musicians. Since developing abc I have heard of several others, some of which are very similar to it.
My own version, however, first appeared in a fledgling form a few years back when I went hitch-hiking around the European mainland. I carried a flute in my rucksack and some tunes in my fingers. Now whilst I can usually remember how they start surrounded by the inspiration of a good session I find it very difficult to get most tunes going sat on my own. I was musically illiterate at the time and so I resorted to writing the first couple of bars of all the tunes I could think of using letters to represent notes.
Some years on, playing French bagpipes in a band, I found I was frequently having to write out transposed versions of tunes before anyone else would learn them. Looking round for electronic help I stumbled across MusicTeX which suited my purposes (almost) perfectly - it was free, versatile and portable to any computer system (and I've been in 3 university departments since then so that was important). It's big drawback is that it involves a lot of work to write out a tune.
I resolved to write a front-end for generating the TeX commands which left me free to choose my own way of writing out tunes. The format I used in the past seemed versatile enough for all my needs and so the software underlying abc2mtex was born (or rather evolved in fits and starts).
I happened to mention this software on IRTRAD-L (the email discussion group for Irish traditionnal music) one day and asked if anyone was interested. A couple of people expressed an interest, most notably John Walsh of the University of British Columbia. It turned out that he had devised and been using a very similar notation system to index tunes. A copy of the software was duly sent out in mid November 93. After several of John's suggestions for improvements had been implemented the first version was released on an unsuspecting world in early December and soon after was uploaded to Ceolas - the newly started Celtic music archive. A few months later in March 94 Don Ward released his package playabc which plays abc tunes through the speakers of various machines.
Updates of the software trickled out over the next year or so and abc gained a small following, in particular on IRTRAD-L. However the spread of the software was always hampered somewhat by the fact that anyone wanting to use it had to install TeX and MusicTeX - no easy feat.
The real explosion in interest came when Jim Vint released his package abc2win in September 1995. The tool was taken up by a large number of the members of IRTRAD-L and abc's of tunes started appearing regularly. More recently (in February 1996) Michael Methfessel released abc2ps which should be portable to any machine with a C compiler. Both of these packages obviate the need to install TeX and MusicTeX and so very much ease the startup curve.
As to the future ... who can say. It seems unlikely that abc can become a universal language for computer music as it is too simple to generate all the notation that would be needed for a modern classical score. On the other hand that simplicity and the fact that it can be "read" and played by humans (rather than just computers) is one of its strengths.
Chris Walshaw