Normally you won't find the Ti-83 Plus graphing calculator sitting beside Nintendo's Game Boy at a museum, but that doesn't mean that a talented developer can't do something incredible with one. Thus: Portal Prelude, a fan-made Portal clone that can be played on Ti-83 and Ti-84 calculators.
The game was designed by an enterprising individual who goes by the name Builderboy. Back in our high school days we used to download simple games for our calculators, but they never seemed as complex as Portal Prelude does. Builderboy even programmed in a story and 38 puzzle-filled levels.
You can download Portal Prelude right here and try it out yourself—but when you inevitably get caught playing during class, you didn't get it from us.