Google's April Fools joke this year is a motion based email interface called Gmail motion. Here's the video that they put on the site:

Whats different about the prank this year, is that there is an acknowledgement that it is actually an April Fools joke. When you click on the 'try gmail motion now' button a popup appears like this:

In previous years, Google have just assumed that people will get the joke, but there were lots of people who actually believed some of the jokes were real, like Goolge Mentaplex - adding a telepathy function to google search, or Google Virgle - which claimed to be training people to live on Mars. Last year it was Animal Translation.