When it comes to fan-fiction, the closest I've gotten is my unfinished novel of a period of a couple of years in the histories of the Merchant Adventurers Company, Thackstones Battalion, 3rd Crucis Lancers and Lindon's Company. Set in the BattleTech universe before it got all broken with the Clans nonsense it details the activities of these units in an offensive during the last Succession War.
I really need to get back to writing I think. I should spend less time in on-line chat and computer gaming and more time creating things again. I've always found it wonderfully theraputic and it's a surprise to suddenly realise what I've allowed to drive it out.