Ambrosia Software (http://www.AmbrosiaSW.com) has released Mondo Solitaire, an US$9.99 solitaire game for the Mac. It requires Mac OS X 10.6 or higher, and a demo is available for download.
Mondo Solitaire has over 300 game variants and an user interface that’s been designed especially with the Mac in mind. In addition to having every solitaire game under the sun, Mondo Solitaire also offers some unique variants such as additional suits, additional decks, and alternate rules, according to the folks at Ambrosia.