From Ippei UKAI:
Hugin is an open-source panorama photo creation tool. It can put multiple photos together very easily and the end result is smooth and stunning. Hugin uses the same open source library used by many other software including shareware like PTMac from Kekus Digital. Hugin is, however, free and you can start making panoramic photos without buying any expensive software or equipment. Unlike many similar software, Hugin considers the shapes of the lens and can adapt to the particular distortion profile of your camera.