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The app store has a few free games. Aside from that, Chrome has a lot of games that you can play and Facebook has their usual selection of social games.
 
There should be a few already on her Mac from Big Bang... Reversi, Tic-Tac-Toe, Mancala, Backgammon, Checkers, and my favorite Chess. And then there's the even better Apple Chess. Pogo.com has a bunch of pretty good Java based games. Yahoo has a good collection too.
 
- Tetris Battle on Facebook
- Super Mario Bros 3 via an emulator
- Pacman (one of the first five google hits)
 
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