I was one of the millions of students who had to use a Texas Instruments graphing calculator in school. I had the TI-84 Plus Silver Edition, in particular. I spent my senior year of high school making tons of games and tools on my calculator. You can program on these calculators with an assembly-like language called TI-BASIC. I was able to automate many of the problems for my classes, but also made some really cool games. I found the loophole where a teacher wouldn't allow phones during a test but would allow a calculator. So when I finished with the exam, I would just play or make games on my calculator. I made about 50 TI-BASIC programs over the years, some better than others.
Below you can see some of my best programs. Click on the name to view the source code then click download to get the file to load onto your calculator.
If you'd like to learn TI-BASIC, I'd recommend this reference guide and this tutorial.