Add mute button to desktop.

So: a Play note button:

A mute button on the desktop and checkbox next each instrument name in the score. That way when you're debugging a score, you won't have to go to the Mixer or anything else. If you have an orchestral score, you would click mute and all checkboxes clear (all instruments become mute), and then you would click on the individual instrument that you want to play by itself. Or you can stop individual instruments from sounding by simply checking the box next to the instrument name and not pressing the mute button beforehand, that way you can have all instruments play except the one you unchecked. So basically you would have one mute button on the desktop, and a checkbox for each instrument generated to the left of the instrument name in the score. You can even make a kind of mute navigator, a small representation of the score and all the checkmarks, that would allow you to simply swipe the checkmarks with the mouse or with your finger on a device to turn a bunch of them on and off with one motion. Let the mayhem begin!