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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Facebook Social Graph
271,051 websites

Facebook Social Graph is free to use

https://www.facebook.com/about/graphsearch

Now you can find more of what you're looking for on Facebook and discover fun connections between people, places and things.

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, Facebook Social Graph 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, Health, Games and 13 other categories.

2 Facebook Social Graph is leading in Arts & Entertainment, Science & Education, Community & Society, Food & Drink and 3 other categories.

Geography

1 Facebook Comments is leading in most countries, including Russia, Vietnam, Brazil, India and 127 other countries.

2 Facebook Social Graph is leading in United States, United Kingdom, Canada, Taiwan and 26 other countries.