MidiKeys 1.9.1

Place a small MIDI keyboard on the screen of your Mac. Press keys on the keyboard or click on the virtual keys with the mouse to play MIDI notes. Play black keys using the keyboard row above, and octaves below using the row starting with 'q'. Connect a MIDI source to view incoming notes played on the keyboard.

MidiKeys shows a little keyboard on screen, and you can use the computer keyboard to play MIDI notes. 'z' through ',' is the octave starting a middle C (note 60). The keys on the row above are flats (black keys), and the octave below is on the row starting with 'q' (and the digit row is that octave's flats).

In addition, you can select a MIDI source and see incoming notes played on the keyboard.