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://openhymnal.org/Abc/

http://abcplus.sourceforge.net/

https://abcnotation.com/tunePage?a=trillian.mit.edu/~jc/music/abc/mirror/musicaviva.com/england/what-shall-we/what-shall-we-1/0000

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/

http://abctunesearch.com/

Thanks to Paul Rosen for his great ABCJS library.