Public Domain Fan Fiction

I wrote about the concept of Public Domain Fan Fiction ( http://www.distasis.com/write/pdff.htm ) in 2005. I've been looking for outlets on and off ever since. I've been aware for a while now of a few forums for writing about superheroes who have lapsed into the public domain. A recent search on science fiction and Creative Commons multimedia brought up some options very similar to what I envisioned back in 2005.

Here are some writing communities that facilitate the creation of a shared universe:
http://www.scpwiki.com/faq
https://www.orionsarm.com/
https://paradisichronicles.wordpress.com/
https://www.thefifthworld.com/
https://witness.scifieconomicslab.net/

If these are out there, I'm sure there must be other groups and forums as well. Feel free to join the wstorm mailing list mentioned on the Public Domain Fan Fiction page and post about your favorite public domain or Creative Commons licensed shared universes.