This is a classic T filter circuit. If you are good at the mechanical side of things you could use this circuit to make a traditional wah wah pedal.
This circuit is also very useful for implementing a notch / sweep filter as part of a music synthesiser. The wah pot would need to be replaced by a voltage controlled mechanism.
The front end of the circuit would benefit from a high Z FET stage to avoid loading down an electric guitar or other circuit. I've published circuits here in EC that would serve this function.
