Author Frederic Shernoff has written a couple of stories and now has contributed a piece of Wool fan fiction to Hugh Howey's world of Wool. Angels of the Earth has gotten great reviews, 4.5 stars out of 5 with 5 reviews currently.
Hugh Howey himself has given this (and many other authors) his blessing and permission to write fan fiction set in his Wool universe.
This is a done-in-one story (meaning this is not part of a multi-series of books), free for a limited time only!
http://www.amazon.com/dp/B00D3A09GO/..._.SBYrb1S81ADV