Déjà is a quiz game with a twist. The basic gist is that instead of answering the question you see on-screen, you have to answer the previous one. It's a good memory challenge, and I hope strikes the fun-infuriating balance well. It's also pretty hilarious to watch someone play it.
I've since taken this app down from the App Store; it had its run and felt like the better move than neglecting it.