Forms and denotators are the language of choice for the music-theorist Guerino Mazzola. I’ve been in the process of writing up a brief explanation/introduction to them, and enough of it is written (10 pages) for me to post it (all that’s missing are one or two fully worked out examples). I didn’t know if I should put it in the maths section, computers section, or music section…but I plomped for the music section (who knows, some day I might add enough on so that it actually contains some proper music-theory :) ).
An introduction to Forms and Denotators: PDF or Postscript.