My TI-85 story involves the fact that it only had 2D plotting (though I think newer models such as the TI-89 had 3D).

I had a 3D calculus class so I wrote a program in it to plot a 3D isometric mesh of a surface using the 2D rendering library. It was slow but got the job done. I used it to help pass a test or two.

I also experimented with drawing random surfaces and objects like a tire. They looked pretty cool for a calculator screen.

The math lab at the college had a cable which you could use to take data off or put it on so you could in theory have exchanged programs with others but this was before the internet so I didn't.

I still have mine and enjoy the sliding the cover off - a trip down memory lane.

Later I rewrote the program in QBasic on a PC for fun and it was lightning fast!