The Bergonzifying Transmogrifier
Pick any four unique notes, one from each of the drop down menus. Choose what clef you would like the variations to be notated in and select what rhythmic value each note should have.
Step 2) Click on the button labeled "Bergonzify!". Nothing will happen until you click "Notate!", so...
Step 3) So click on the button labeled "Notate!" already! Now you can see (and hear!) all the permutations of the four notes you selected. Click on the examples to access the playback feature and transposing options.
Read more about this thing and ideas on how to use it here.
Additional details here and here.
Update: 07/31 - Added rests to note selection drop downs.