From the "If You Can't Beat Them, Make An Add-On' files:

Google today released a new open source effort that aims to bring advanced web technologies to Microsoft's Internet Explorer browser.  The Chrome Frame effort is a plug-in for IE 6,7 and 8 that brings HTML 5 and enhanced JavaScript performance for IE users.

That's right, IE users (even IE 6 users) don't have to use a different browser to get some Chrome goodness. They can just get the Chrome Frame plug-in and use their existing IE browser.

Why is Google doing this? Why not just focus on getting users to migrate to Chrome or Firefox? The answer provided by Google shows me that Google is a realist when it comes to browser shares.

"Recent JavaScript performance improvements and the emergence of HTML5 have enabled web applications to do things that could previously only be done by desktop software," Google blogged. "One challenge developers face in using these new technologies is that they are not yet supported by Internet Explorer. Developers can't afford to ignore IE -- most people use some version of IE -- so they end up spending lots of time implementing work-arounds or limiting the functionality of their apps."

Now to be fair, IE 8 does support a number of HTML 5 features and has better performance than IE 7 or 6. That said, IE 8 does not support every single HTML 5 feature that Google Chrome supports today.
So in one swift stroke, Google's Chrome Frame could now be the engine behind IE. It's astounding isn't it?