Lessee ... I was into 'Project A-Ko' (anime), 'Ranma 1/2' (manga/anime), 'The Big O' (anime), 'Harry Potter', and then 'Doctor Who' (my own version of 11 back in 2007). I dabbled in writing scripts for 'The X-Files' back in high school. The last so-called fanfiction I wrote was a steampunk sequel to 'Alice in Wonderland'.
Any of my stuff that somehow ended up online - either by my ex-husband or my best friend's doing - usually had huge fan followings and accusations of being one of the writers of the show ... in point of fact, I was accused by friends of being one of the writers of 'Supernatural' because I wrote that type of stuff. I hadn't even heard of it at that point.
I like playing in others' universes. I tend to make logical extrapolations on minor details that end up changing the direction of the series or world. Not to mention address some subject matters that the real writers either won't or can't tackle ... this may be the reason I was accused of being a show's writer.
Haven't done it for a while, except for 'Alice'. I lost my interest in fanfiction writing when my ex-husband and I separated and divorced. He was my writing partner.