The 'Another Realm' series of self-insert fics set in the Mass Effect (original trilogy) universe, increasingly alternate-reality as it goes on. It no longer exists online as far as I'm aware, as the author adapted the story for his own original universe and has to date released eight books set in that universe. Six of which are rewritings of the original fanfic including a conclusion of sorts, two are a separate series (for now) set in the same universe, and there's also another series written by another author set in the same universe which is also a rewriting of a finished fanfic originally set in the AR universe.
The original adaptation universe is called 'Knights of the Compact' I think, and the initial series of novels following Cieran Kean is called 'The Lost Knight', if anyone's interested. They are quite good, I've enjoyed them immensely.