Fan fiction has, arguably, existed in some form since 1614, and it has certainly been in existence since the Star Trek fanzine, Spockanalia was published in 1967, while derivative works and unofficial adaptations have long existed (such as Edison's Frankenstein) in the mass market, most obviously Nosferatu (unofficial trailer, whole film) and the infamous Tijuana bibles, but in the modern world of extended copyright and Internet commerce are fan fiction and fan art legal?
Like short stories but just don’t have the time to hang around for ten, five, two, or even one thousand words? Try some drabbles, stories precisely 100 words long. There was a bit of a craze in the early 90s, but some enterprising websites (including the successfully-published Brendan Adkin at Ommatidia) are still updating today (Previously). Write your own! (For the terminally lazy, automatically generate one instead.)