ZTetris (1996)

ZTetris is the classic TI calculator clone of the popular Tetris game that everybody has played, and that has been made for all kinds of gaming platforms. The original game was programmed in assembly by Jimmy Mardell for the TI-85 and executed via ZShell, but the game has since been ported to every TI graphing calculator by other members of the community. The game has an impressive list of features, including two-player linkplay (which even works between every TI graphing calculator), 21 levels, top 3 high scores saved with names, 16 different alternating background patterns, trash lines, and even a teacher key.