Apple has started seeding developers with an early version of Safari 4 (5526.11.2). The release comes amidst news of Apple's plans for Mac OS X 10.6 (Snow Leopard) which will focus on performance and quality.

In their press release for Snow Leopard, Apple revealed that Snow Leopard includes Safari "with the fastest implementation of JavaScript ever, increasing performance by 53 percent, making Web 2.0 applications feel more responsive." Apple will reportedly accomplish this dramatic speedup with SquirrelFish technology which is currently under development for Webkit. Snow Leopard is due for release in "about a year", though Safari 4 release could come much sooner and for existing operating systems. In fact, they are seeding versions specifically for Windows, Tiger and Leopard.

Apple's focus on high performance JavaScript becomes obvious now that they have demoed the new web applications that come with MobileMe (Guided Tour). MobileMe provides web-applications for email, calendar and address book which were described as being as responsive as desktop-based applications.

One new feature found in Safari 4 is the ability to save webpages as stand alone "web applications" which launch much like regular applications. This replicates functionality found in Fluid, a Mac OS X Leopard application which creates these Site Specific Browsers.

Required update to 10.5.3

You can download this build ***link deleted****

Can this be installed along side Safari 3? Or can you only run one or the other?

I've just installed it on my Hack running Tiger 10.4.11, it looks like it replaces 3.1.1. There is an uninstall package with Safari 4 just in case. I've had no problems and I'm using it right now