[LAU] Teaching tool to visualize waveforms?

Hello, all, I'm talking an Introduction to Audio Processing course at our local community college. In our third class, the instructor presented visually waveforms, using Apple ProTools, and we listened as they combined. The examples showed equal frequency waves with a phase delay, showing cancellation and amplification. We also listened to the beats of waves at frequencies like 440 and 445 or 450Hz. Finally we listened to pure sine wave, then the wave with 2nd, 3rd, 4th, 5th, etc. harmonics. However, we never saw a visual representation of the combined waveforms. As a former teacher, I thought it would enhance the lessons to also visualize the waveform. I think this could be done in Audacity, by mixing the waveforms to a final track, and viewing it. However, I think this would be somewhat clumsy. I also think that I could do this in GNU Radio, with mixing nodes and oscilloscope displays. Can anyone suggest a tool that would allow visualization of waveforms based on combined sine waves? My ideal setup would allow sliders to change the parameters, say, the phase delay, or frequency difference, in real time, and continuously display the combined waveform. Any thoughts or guidance is appreciated. Thanks for your advice. -Kevin