MacSolitaireX is a free, open-source “klondike” solitaire game for Mac OS X.  Users of Windows Solitaire should be very familiar with the interface, options, and gameplay.  Available options include one or three card drawing, timed games, and both standard and vegas scoring.
MacSolitaireX is written in Objective-C++, and makes use of the Cocoa user interface library and uses OpenGL to render the playing area. Update 1.1 brings new card deck images courtesy of James Badcock. Also, there was a minor bugfix that resolved an issue with incorrect scoring after winning a game.