From Tatooine to the jungle moons of Endor, from Jar Jar to Jawas--the mythical cosmos of the Star Wars universe is truly vast, strange and diverse. Many of these come from the realm of Star Wars canon, commonly known as the "Expanded Universe" and much more recently as "Legends," which might be considered "semi-canon" in the sense that they're being utilized as motivation for future Star Wars storylines but may not be carved in stone.
Most of these are not, however, simply fan fiction. Some stories were written by someone who was paid a lot of money by George Lucas. In many situations, they would've been better off purchasing the copyright to the greatest fan fiction ever.
Back in the days of the Original Trilogy, the Star Wars universe's basic logic was impenetrable. It's impossible to take apart the scientific inconsistencies of a cosmos populated by space samurai wizards and psychic puppets.