Auth0 is an identity-as-a-service platform for developers. You can use Social Providers (Like Facebook, Google, Twitter, etc.), Enterprise Providers (Active Directory, LDAP, Windows Azure AD, SAML, etc.) and a Username/Password store which can be saved either by us or by you.
We have SDKs for the most common platforms (Ruby, Node, iOS, Angular and others) so that, regardless of which application you write and what language you use, you can get the Authentication implemented with a couple lines of code.
Auth0 value proposition is to remove the complexity of Authentication and Authorization, so that developers can spend less time writing plumbing, and more time building great features.