Tetris Program.  I would guess that the original programmer (Alexey Pajitnov) was sitting in front of a Russian machine in the early 1980's that was very similar the Interak. (maybe a terminal)  And so I decided that I would like to follow in his footsteps in a way, just to experience the same kinds of questions and answers that he must have experienced.

I had never seen any Tetris code but I had a slight advantage over Alexey in that I already knew how the finished game should operate.
At first glance it seems like a simple enough game but when you consider that the program has to deal with tumbling blocks of various random shapes it starts to become more involved.  It was like a 'clean room' approach where the end result is the same but the coding is quite different.  (Bill Gates and Gary Kildall ?)

Screen dump during development, showing each of the Tetris shapes and the playing area.  To see the game in action click this link...http://www.youtube.com/watch?v=UXXHAbTR_iY