Go Fucking Do It - Set a deadline and a price. If you fail, you pay.
ToT: ThisOrThat - Let your friends choose this or that for you
Decidr - Make better decisions with quick A/B polls
sup - The first creep-free way to see nearby friends
AbTest.io - A free url shortener with A/B testing features
Mu4e - Starting with version 0.9.8, mu provides an emacs-based e-mail client which uses mu as its back-end: mu4e.