One of the main issues a web developer is faced with, is to ensure that his (hers too!) work renders correctly in all (most) of the browsers in use.
Of course, there is always the wonderful browsershots.org, to which you can submit your URL(s) and it will show you what your page will look like any every single browser known to man!
But if you wanted instant gratification, you could, say, install all 'other' browsers on your desktop and then pick one version of IE to work with. You could never use more than one.
However, since the advent of 'virtual application' tools, such as VMWare's ThinApp and Xenocode, things have changed!
You can now wrap up an app, such as IE6 (also known as Internet Embarassment or the curse of MS upon web developers) into a single EXE that is, in effect, a standalone application.
And that is exactly what Xenocode have done. They have wrapped up Safari, Firefox, Chrome and IE6, 7 and8 into standalone EXEs which you can download and run, without having to install anything!!!
And you can run all of the Internet Embarassment versions at once!
For more info, visit Xenocode
[Update 6 june 2011] It all seems to have gone to the doghouse. The EXEs have long since been removed.
The new website is called Spoon.net...]