Mario Teaches Typing is a child-oriented typing program that was released by Interplay in 1991. Building on the success of previous video games featuring the Mario Brothers, you can lead Mario, Luigi or Princess Toadstool through perilous environs by pressing the correct letters.
The first level teaches you the keys row by row while you hit blocks and jump on Koopa Troopas. In the second level you are avoiding squids with arms and Boss Bass by typing in actual words. The last level has your character running through Bowser's Castle avoiding Thwomps and swimming through quicksand while you punch out whole sentences. If you reach your goal WPM using all of the letters, numbers and symbols then you can go to the next level and you get to print out a nifty certificate to put on the refrigetrator.
As much as I enjoyed this program back in the day, it does have its limitations. Accuracy has no effect on gameplay (other than being stuck indefinitely in front of a turtle), and the lessons are of definite time instead of a set number of letters or words, which means that sometimes you don't get to all the letters you're supposed to be learning before time runs out. Even still, I think it's an excellent program and is one of many reasons I hope that the computers of the future still have DOS.
http://www.the-underdogs.org/game.php?id=1333 (download available)