FanFiction.net is the grandfather of the fanfic world. It’s a bit dusty, the interface is a relic of 1998, and it lacks the sophisticated safety tags of its younger, more popular sibling, AO3.

For a teen who loves to write, it's a goldmine of inspiration, but for a parent, it’s a site that requires a high degree of trust. There is no 'Kids Mode' here. If they’re using it, they’re going to see things that aren't in the original books. It’s a great tool for budding writers, provided they know how to hit the 'back' button when things get sketchy.