MusicXML

MusicXML is a file format for specifying sheet music. It can be used in a similar way to MIDI. There are many available programs for generating it, and the spec is widely used, highly documentated, and mature.

There are many programs available for reading/writing MusicXML:

• Finale Notepad (I used this like 10 years ago but apparently it's still around)
• Cadencii, popular in the [utau] community for producing input for [vocal-synthesis] programs like [sinsy]: http://utaforum.net/threads/cadencii-download.2429/