DaCapo Editor is a music sheet editor based on the ABC syntax with which you can write easily music scores and partitions.
Find the application here: https://man-schu.github.io/dacapoeditor/
A standalone desktop version based on Electron can be downloaded on https://github.com/man-schu/dacapoeditor/releases/latest/.
http://abcplus.sourceforge.net/abcplus_en.html - a full manual by Guido Gonzato
http://www.stephenmerrony.co.uk/uploads/ABCquickRefv0_6.pdf - a reference card by Steve Merrony
https://abcnotation.com/wiki/abc:standard:v2.2 - reference by Chris Walshaw, the inventer of the ABC Syntax
https://elmu.online/articles/hilfe-abcnotation (in German)
http://kurs.schacherl.info/ABC-Musiknotation/abc_syntax/abc_syntax.html - an extensive manual in a downloadable html file (in German)
https://www.biteyourownelbow.com/abcnotation.htm - a very short introduction
http://abcplus.sourceforge.net/abcplus_en.pdf - manual for ABC plus
https://abcnotation.com/examples
http://abcplus.sourceforge.net/
https://sites.google.com/site/lotroabc/songs
https://abcnotation.com/tunes - a list of tune collections
https://abcnotation.com/search
http://trillian.mit.edu/~jc/cgi/abc/tunefind
http://john-chambers.us/~jc/cgi/abc/tunefind
https://www.folktunefinder.com/
Thanks to Paul Rosen for his great ABCJS library.