Microsoft's newly launched IE8 beta download

Internet Explorer 8 beta release is for developers, and Microsoft's
Dean Hachamovitch promised at MIX08 that IE8 will make it easier to
build Web sites for multiple browsers and stop wasting developers'
time. Microsoft's IE8 features Activities for looking up information
and Webslices to watch portions of Web sites for updates.

more about MS

That's odd, there doesn't appear to be a Linux or Mac OS version for download:

So I guess it's not for _all_ developers..

Hi, Microsoft has discontinued IE for Mac OS. Furthermore, it seems clear that Microsoft only intends to support Windows OS for IE and I wouldn’t hold my breathe for other operating systems.

Good luck,