Persona

 Persona  was an email-based authentication service from Mozilla that was supported by IndieAuth for rel-me links to email addresses; it was shut down November 30, 2016. 

Persona is based on the BrowserID protocol for authenticating users based on email address.

Some fans of Persona have started a "spiritual successor" called Portier.

IndieWeb Examples
Examples of IndieWeb sites which act as their own Persona provider, without relying on delegation to another email provider, or to the Mozilla default provider.
 * ... add yourself

Examples of IndieWeb sites which consume (allow login via) Persona in particular (beyond using IndieAuth to do so).
 * tommorris.org - although people other than me don't really get to do much other than enjoy the fact that it says "You are signed in as {your email}".
 * 2017-02-21 - functionality removed following Persona shutdown - switched to IndieAuth

Shutdowns
The following sites used to provide or accept (consume) Persona logins but no longer do. Most recent first:
 * 2014-06-10 orchestrate.io is phasing out Persona login. The next time you sign in they require you to set a password.

Shutdown of Persona services itself:
 * Mozilla Wiki: Identity/Persona Shutdown Guidelines for Reliers
 * Mozilla Wiki: Identity/Persona AAR "Here's a summary of what we got right and what we could have done better with Persona, distilled from a lot of different conversations with people inside and outside of the core team."
 * 2014-03-08 Hacker News: https://news.ycombinator.com/item?id=7364465

Reliance on JavaScript
Persona/browserid relies on JavaScript to work, forcing consumers to implement separate authentication functionality to support all users (e.g. users without JavaScript or when it fails to load).