Facebook Comments
333,844 websites

Facebook Comments is free to use

http://developers.facebook.com/docs/plugins/

Facebook's Comments box lets people comment on content on your site using their Facebook profile and shows this activity to their friends in news feed. It also contains built-in moderation tools and special social relevance ranking.

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Pinterest
292,411 websites

Pinterest is free to use

http://pinterest.com/

Pinterest is a social networking site with a visually-pleasing virtual pinboard interface. Users collect photos and link to products they love, creating their own pinboards and following the pinboards of other people whom they find interest...

Market Share by Top Websites

1 Facebook Comments is leading in Top 10K Sites, Top 100K Sites, Top 1M Sites and The Entire Web.

2 In terms of market share, Pinterest is clearly lagging behind, losing to Facebook Comments in all segments.

Websites Categories

1 Facebook Comments has better usage coverage in more websites categories. Including Computers Electronics & Technology, News & Media, Science & Education, Games and 8 other categories.

2 Pinterest is leading in Food & Drink, Arts & Entertainment, Lifestyle, Home & Garden and 8 other categories.

Geography

1 Facebook Comments is leading in most countries, including Russia, Vietnam, Brazil, India and 129 other countries.

2 Pinterest is leading in United States, Japan, France, United Kingdom and 26 other countries.