Droneo is also getting an upgrade in a week or two maybe, with this cool new feature:

You'll be able to set up the intervals via this tone spiral (which will look better ...
The black spiral represents logarithmic interval values, each cycle of the spiral is an octave higher, these spokes are the 12-ET scale. (that's why they are equally spaced) There will be a menu of choices to help you choose tones, and also a snap button. you just drag the circle (reed) to the interval spot of your choice. This is really interactive and can be played as an instrument. More to come!