The long-sought-after fourth component has been found!
Seriously. No, I'm not joking.
It's called a memrister.
And it's going to render every electronics/circuits book in the world obsolete. Well, maybe not obsolete, but definitely in need of revision. I'm not going to bother discussing its merits/uses in this post. The articles do a darn good job of that.
But please feel free to start a discussion in the comments.