Recently Facebook has announced the launch of its new mail program that is dubbed to be the Gmail killer. Many say that it is similar to Google wave and Facebook states that it is meant for emailing and chat as opposed just to another email program like hotmail, ymail and or gmail.
Honestly I believe that when someone names something the "X Killer" it is a desperate move in order to create a buzz about the product. You never see the bigger company such as McDonalds advertising

McDonalds Recipes