The main Omniocular collection is for non-challenge fics posted to the comm by members, and there are 19 sub-collections for fics from every challenge we ran that got entries.
The collection and subcollections are moderated, but as long as we can find the fic in the archive or memories of this community, we will accept all submissions, from community members and non-members alike.
At this point, the AO3 is not hosting art, so the collection is for fic only, but we hope in the future that we will be able to include art as well.
To learn more about collections on the AO3, including how to add fics to a collection, please read the AO3 Collections FAQ.
If you don't have an AO3 account, you can add your email address to the waiting list here.