The Good Omens Library: A Nice and Accurate Stories Archive, first opened in 2005 as a hub for Good Omens fanfiction. After eight years, decreased funds and usership nearly closed the archive for good. To preserve its works and allow the collection to continue to grow, it was imported into a new AO3 collection in 2013.
Read (or edit!) the The Good Omens Library article on Fanlore.