So Yahoo bought Oddpost a while back.
Oddpost developed a killer web-based e-mail application that was way ahead of its time... basically, all of the functionality of Outlook in a web-based application. Clearly, Yahoo saw the value in it...
Now Yahoo is running a beta test of a new Yahoo Mail interface that incorporates Oddpost's technology.
Check out the screen shots below.
Y! Mail Beta - a photoset on Flickr