The nifty Stack Exchange is mostly a knowledge-sharing network where programmers help one another out with gnarly coding challenges. But the geeks who gather there have a deep interest in fiction and film starring Hobbits, Jedis, vampires, mutants and other fantastic creatures. At Science Fiction & Fantasy Stack Exchange, they engage in spirited discussion of questions from the purely practical (“Should I watch The Avengers before going to see Iron Man 3?” to the profound (“Why was the Balrog unconcerned with the fate of Middle-earth?”)