Apple releases Safari 4 Public Beta today. It is available for Mac OS X (Tiger and Leopard) and Windows (XP and Vista).
Safari 4 Public Beta includes Nitro engine and slew of new features such as Top Sites, Full History Search, Cover Flow, and Tabs on Top.
Check out the new Safari Welcome Page (Safari 4 Public Beta or the latest WebKit is required to make this page work.)
Get it from http://www.apple.com/safari/
WebKit, the Open Source counterpart of Safari is available from WebKit.org.