MidiKeys is a small application for Mac OS X that presents a miniature MIDI keyboard onscreen. You can use the computer keyboard to Play MIDI notes, or click on the keys with the mouse. There is also an option to select a MIDI source and see incoming notes played on the keyboard.
The keys 'z' through ',' is the octave starting a middle C (note 60). The keys on the row above are flats, and the octave below is on the row starting with 'q' (and the digit row is that octave's flats).
In order to hear a sound when you press keys, you need to connect the MidiKeys output to a synthesizer of some sort. This can be either a softsynth like SimpleSynth or a hardware synth Connected through a MIDI I/O box. MidiKeys has no way to produce sound on its own.
