The Stratolaunch project was started back in 2011 as a joint corporation between the Microsoft Co-founder Paul Allen and the founder of Scaled Composites Burt Rutan. The Stratolaunch has a wingspan of 385 feet and had a special fully customized hangar built solely to accommodate its size. This project was not primarily started to create the world's largest airplane, but it was designed to used in rescue missions in affect parts of the world in the event of a natural or man-made disaster to carry the necessary aid resources. Its scheduled to take its first flight soon and book its place in the record books.
Here is the airplane in all its glory:
Image Credit: CNET