Supported social networks and OpenID providers:

Google, Google+, Facebook, Twitter, Vkontakte, Mail.ru, Odnoklassniki, Yandex, Rambler, LinkedIn, Yahoo, MyOpenID, Live Journal, Flickr, WordPress, Blogger, Verisign, Dropbox, Foursquare, Instagram and others.

Cackle for Joomla

Uses Cackle API
Comments indexable by search engines (SEO-friendly)
Auto-sync (backup) of comments with Cackle and Joomla database
Custom html for seo
Comments counter in categories
Support Single Sign-On (SSO)

Cackle Features

Share on Vkontakte, Mail.ru, Facebook, Twitter, LinkedIn
Multimedia attachments (PNG, JPG, YouTube, Vimeo, SlideShare and other...)
Moderation comments through widget, without leaving your site
Threaded comments and replies
Notifications and reply by email
Anonymous commenting
Powerful admin tools
Ban by IP, User
Nasty words filter
UI Editor to customize widget