Drone MIDI Files
Here are MIDI files in all 12 keys with open drones.
By playing just the two skeleton notes of a key or chord (the tonic or root, and the dominant or fifth), the drone gives you the tonal background to play a wide variety of major, minor and modal scales, arpeggios, chords and melodies. This can help you stay grounded in a key and in tune while practicing. It can also help you explore unfamiliar key positions, techniques, and musical materials by putting them in a tonal context.
To hear a drone, just click on the key you want. To download it, right click and follow the menu.