Facebook Social Plugins
3,185,744 websites

Facebook Social Plugins is free to use

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

See what your Facebook friends have liked, shared, or commented on across the Web. This includes all variations of Like, Share and Follow Buttons, Embedded Posts, Comments, Activity Feed, Recommendations Feed, Recommendations Bar, Like Box...

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Twitter
1,822,727 websites

Twitter is free to use

https://twitter.com

All Twitter's social tools, including buttons and timeline widgets.

Market Share by Top Websites

1 Facebook Social Plugins is leading in Top 1M Sites and The Entire Web.

2 Twitter is leading in Top 10K Sites and Top 100K Sites.

Websites Categories

1 Facebook Social Plugins has better usage coverage in more websites categories. Including Computers Electronics & Technology, Arts & Entertainment, Science & Education, Food & Drink and 18 other categories.

2 Twitter is leading in Games and Adult.

Geography

1 Facebook Social Plugins is leading in most countries, including United States, France, Italy, United Kingdom and 160 other countries.

2 Twitter is leading in Japan and South Korea.