Multi-Fandom Fan Fiction

If it's a story you were writing for someone, I'd class it as a ficathon story. If it's a story that was just a general challenge, that didn't have recipients as such, and there is nobody waiting for the story (anymore), then I guess it would count as an unfinished story. That is, if you happened to get the idea for the story from a challenge, but you didn't actually participate in the challenge, then it's "your" story.