I have great affection for most monome apps.
But I’m very fond of Monome Notes because it is often the fastest way to make the monome do something musical with other musical devices I’m working with at the time.
The app author, myr, describes it:
monome notes is an app for playing midi notes on a grid device. it turns each key on the grid into a midi note which you can trigger by pressing the key, similar to a keyboard or drum pad. the app allows you to control the way the notes are laid out and displays information about the current note layout on the leds.
it’s kind of like a guitar fretboard, where you can change the tuning between strings, change the distance between frets and even snap it to play in a scale; all the while the fretboard can light up to show you whatever scale you select.
you set the interval between each column and row in semitones (or scale degrees if snapped to scale), relative to the first note in the grid. the first note in the grid is set by the offset number. you can set a scale using the drop down menu, set the root note for this scale to start on and snap to the scale eliminating all non-diatonic notes from the grid.