Mozilla Persona — an identity system for the web

It looks really promising:

At Mozilla, we believe that your online identity should belong exclusively to you. With that in mind, we created Persona to improve the way you sign in to websites.

Persona allows you to sign in to sites using an email address you choose. So, instead of having to manage multiple usernames and passwords across your favorite sites and devices, you’ll have more time to do the important stuff. We’ll manage the details!