Bring out your inner Beethoven:
1. Hold down a pitch (QWERTYUIO[]\ASDFGHJK keys).

2. Press 2, 3, 4, 5, or 6 to write out different durations.

3. Make them rests by holding down the zero key in your numpad, or dotted by holding down the period key in your numpad.

4. Fix up any pitches by pressing the up/down arrow keys, or any durations by pressing the +/- keys. Move around by pressing the left/right keys.

Works best in Google Chrome, the free and best HTML5-compatible browser from Google.