If you have Firefox: this is a machine that makes sounds. It's not a very serious project, but I find it entertaining. Click and drag the dots in order to move the levers, and click the play button to hear the result. (Further changes are not picked up in real time; you have to click play again.)

Try this:

Bubble music

Curious drill

Beach things

Click the eye icon for more examples (be prepared to turn down the volume).

'vib' is vibrato, causing the pitch to change pitch over time.
'trem' is tremolo, causing the sound to become quieter and louder over time.
'vib10' and 'trem10' are more potent versions of 'vib' and 'trem' (the frequency is 10 times faster).
trem10 with a high frequency can be an interesting effect. vib10 with a high frequency can in effect use frequency modulation to create another pitch.
vibc is the cooing of a bird; it plays one quarter of the vibrato and silences the rest.

The smaller control to the right of the modification type can adjust phase.

The button on the left, above the eye, will enable 'layer audio'. Now whenever you click play, you hear the previous results too, and can layer sounds upon sounds.

To make fine adjustments, click the textfield button to manually enter a value. Alternatively, click save and make adjustments to the data in the url.

Try it!
(Chrome or Firefox only)