Jan Kees van Woesik and Patrick Brouwer have made a system to control Flash with audio.

Jan Kees writes:

We have created an alternative approach for this (worldwide) known problem. We made a MaxMSP patch that does the FFT analysis and sends a OSC package to flash (with the help of a small java application). MAX/MSP sends the Amplitude and the pitch of a stereo signal (left and right). So, now we could use the input of the microphone to make a two-player game. If you only have one input they will both send the same data. In fact you will only get four parameters in flash, you can do whatever you want with it (be creative)!

James Howard Young’s modified Pong, using microphone input and live video tracking

Check 6 Angry Men for more information and a link to download the source files (Creative Commons Share Alike 3.0 License).