This project contains the source code for a web-app which combines a keyboard-centric workflow with GUI elements to serve as an engraver of sheet music.
More traditional approaches use widgets and other GUI elements to act upon the piece of music (check out MuseScore). Others like LilyPond take the programmer route and provide and a compiler which generates music from a source file.
While far from being as complete as the previous two examples, this app can still be used to engrave certain types of pieces. Its strength is quickly drafting sheet music but not necessarily chiseling the finer details.
Below is a showcase of some of its features.