I had a TI-85, and because it only had 2D plotting while the TI-89 had 3D plotting, I decided to write my own 3D plotting program. I allowed the user to input

I had a TI-85, and because it only had 2D plotting while the TI-89 had 3D plotting, I decided to write my own 3D plotting program. I allowed the user to input a 3D equation, and then it would draw a mesh using trig to project it from isometric 3D to 2D and render it on the screen. It was very slow, but it worked! I even used it for one of my calculus classes. It made very pretty graphics. I later ported the algorithm to Visual Basic just for kicks, and it ran a lot faster on a PC. In the process I learned a ton about programming and trig.