bubl is a simple FFT spectrum visualizer for Windows. The bubbles generated correspond to spikes in the FFT spectrum of your microphone input, where higher frequencies produce bubbles further to the right, and larger bubbles indicate greater quantities of that frequency. The waveform of the current microphone input is also rendered as the surface of the "water" the bubbles are drifting in.
bubl was developed in OpenFrameworks in Code::Blocks under Windows 10. Ports to other OpenFrameworks environments should be relatively straightforward.