Thanks for taking it for a spin! I should include an in-app notification for web users... due to the limitation of running on web (unable to write files to a file system) the music data cannot be saved into MML which is then used for audio playback.
In the future, I hope to be able to make the audio playback independent of the MML export flow so that web users can also enjoy their tunes. I'll be exploring what can be done safely via browser.