I didn't imagine you could create music with a TI-81 style calculator, but seems I was lacking in imagination:
This seems to be a basic sequencer style of music, but the results are quite charming.
When I was watching this, I first thought the calculator was going to play tones that corresponded to the equations... the person who made this video apparently pursued that idea and created Equations: Graphing Calculator Synthesizer.
Where mathematics meets music: a unique synthesizer plugin that puts the power of mathematical expression directly at your fingertips. Instead of selecting from preset waveforms, you write your own equations to generate completely unique sounds.
Pretty interesting stuff!