Free. Requires a Mac with a 500MHz Intel processor, 512MB of RAM, Screen resolution of 800x600, Mac OS X 10.6 (Snow Leopard) or 10.7 (Lion), 100MB of available disk space.
Free. Requires a PC with a 500MHz Intel or AMD processor, 128MB of RAM, Screen resolution of 800x600, Windows XP Service Pack 2 or later, Windows Vista or Windows 7, 100MB of available disk space.