The story of the apple, Newton's head, and their chance encounter that yielded the theory of gravity is well known. Some have questioned if it happened just that way, but though he only mentions seeing an apple fall, not having it fall on his head (this appears to have been added by Isaac D'Israeli), the tale appears to originate with Newton himself, told to his friend William Stukley in 1726. This is, of course, roughly sixty years after the event, which occurred when he was a twenty-two year old avoiding plague-ridden London at his family home, Woolsthorpe Manor.
Whether it occurred the way Newton claimed (or at all), we may never know, but Woolsthorpe Manor did (and does) have a number of apple trees. The tree which dropped this particular apple was of cultivar called 'Flower of Kent', a variety of which several remain at Woolsthorpe. The actual tree lived a long life, but is long gone today. By 1814, it was heavily decayed and collapsed, propped up along the ground. In 1820 it was badly damaged by a storm and was taken down. A local teacher sawed the tree into pieces, many of which were kept as souvenirs. One piece was presented to the Royal Astronomical Society in 1914, another appears to have been made into a pair of rulers, award to a member of the Royal Society in 1844.
'Flower of Kent', despite its name, did not likely originate in England, but rather in France. It is a cooking apple, somewhat smallish, and of an unusual pear shape. By all accounts it is mealy, subacid, and rather flavorless.
Today, the cultivar is largely forgotten, although a handful of trees remain, and many can trace their provenance directly to Newton's famous tree. After Newton's death in 1727, the new owners of Woolsthorpe Manor sent budwood to Belton Park, in Lincolnshire, and from there it was passed to the research station at East Malling. In 1944, grafts from the trees at East Malling were planted at the home of William Penn in Morrisville, Pennsylvania, and it is these trees which are the sources of most, if not all, of the 'Flower of Kent' trees in the U.S. (Antique Apple Orchard in Oregon is the only commercial operation I know of with it). The same source in East Malling are the origin of the first 'Flower of Kent' in Canada, recently planted in York University. (Siloam Orchards, who propagated it for the university, appears to have it too.)
(By the way, yes, I'm still alive...just really busy trying to get as much research done as possible before daughter #2 arrives on the scene. And, along with my daughter, enjoying a nice round of strep throat right at the moment. Just saw this and thought I'd post it, though).