"The Female Man" by Joanna Russ
It was... a book. I can't really say much more, because to say that it was good or bad, I'd have to understand it. I read the description on wikipedia afterwards and while I remember most of the stuff mentioned there, there were whole chapters I still have no idea what they were about.
So: A great premise (four people, who are the same person just from different realities, meet), but a very confusing book.