OK, so Portal is not what one would call a casual game, but hear me out. Valve has released Steam for Mac in addition to PC. Steam is an online web site and platform to buy and play download games, of which there is a sizeable and growing casual games section.
Until May 24, 2010, when you download Steam, you’ll get Portal for free. Admittedly, Portal is a first person shooter/puzzle. But, it’s really good and has been played by millions and millions of players online. And what is not a casual game, but a game designed to be played by everyone?