IBM gained fame in this supercomputer arena with their Deep Blue computer, beating world chess champion Garry Kasparov two games to one (with three draws) in a six-game match. This was the first time a computer had ever beaten a human chess champion. Kasparov apparently was so upset that he demanded a rematch, but IBM ended up dismantling the Deep Blue computer.
Rather than focusing on known chess moves, Watson can understand natural language, and then play competitive games of Jeopardy! by providing the correct answers (in the form of a question, mind you). You can actually play against Watson through the IBM website (I got my butt stomped, by the way…)