Chrome to Phone comprises a Google Chrome extension and a Google Android app, which connects your desktop with your phone in the way that was demonstrated earlier this year at Google I/O. Essentially, sending tasks to your phone.
It was built by Dave Burke, Engineering Manager, in his spare time.
This is the Android's cloud-to-device messaging, so it can know what you're sending to your phone and will optimize what it's showing. For example, if you're watching YouTube, it'll send a YouTube link to your phone and will automatically start playing the video. Another is if you're reading a page on the browser, it'll load up that same page on the mobile browser.
Another example: Google Maps. Browse a location on Google Maps on the desktop and it'll bring up the same location on Google Maps on Android. The same thing works with driving directions. How about searching for business on your desktop and having to manually dial the number from your phone? This will take care of that too, and will immediately launch the dialer and dial up the business you just searched for.
It is now available for all users on Froyo, and will be open source so any developer can use it (it's built on Google developer tools). FoxToPhone, an extension that makes FireFox play nice with the ChromeToPhone app, is already available.
Google says they're "looking at" bringing this to the iPhone, but they haven't submitted any such app to the App Store, and won't go into any sort of detail (as expected). Seems unlikely!