Reddit user Builderboy2005 has created his own version Portal for use on Texas Instruments graphing calculators (the TI-83 and TI-84 specifically). While we have seen past works of porting video games to calculators, it's especially amazing to see the space-warping mechanics of Valve's hit game working on these devices.
Titled Portal Prelude, this side-scrolling platformer contains 38 test chambers for you to play through, and it doesn't miss a beat of it's official counterpart's physics-based gameplay with the help of your trusty Portal gun. The creator has said it took several years to complete, and his meticulous attention to detail shows through everything from the variety of puzzles, to the interspersed dialogue that occurs in-game.
Quite a feat of game design. Feel free to download the game for yourself.