References
The problems with Traditional Notation
Concerns with Traditional Notation Rhythm Notation
Gardner Read's book "Source Book of Proposed Music Notation Reforms"
the Music Notation Modernization Association (MNMA)
The Music Notation Project forum
The MuseScore website has a wide range of scores in MusicXML format available for download; scores in the public domain are free while others require a membership subscription.
Klavarskribo Institute home page
Klavarskribo Documentary – Part 1 (1974)
Klavarskribo Documentary - Part 2 (1974)
Klavar Facebook group "Synthesia on paper!"
Klavar Facebook group Sheet Music and Software
Klavarskribo sheet music display app
What You See Is What You Play (WYSIWYP). I confess I have my own entry in the Alternative Notation arena and here are some links that describe and promote it:
A succinct description of it on the Music Notation Project Wiki.
And of course, a pitch of its own where I make the case that it may be the best choice for adult beginning students of the piano.