Intended to be a space for blogging and discussion, in the early 2000s LiveJournal became the place where everyone aired out their drama and wrote fanfiction.
A weird, constantly breaking website that became the compendium of everything. Since personally-hosted, fandom-specific websites fell apart, this became the place to hold and host mostly all of the fanfiction.
Run by the Organization for Transformative works, this is the best of all possible fanfiction worlds. It allows free posting and the OTW has a legal arm that protects fans from copyright claims taking down their freely posted work.