Embedded Tweet feature allows websites to generate copy and paste-able HTML markup to render a Tweet on any third-party website.
https://dev.twitter.com/docs/embedded-tweets
Widgets
Get access to data on 224,449 websites that are Twitter Embedded Tweets Customers. We know of 38,103 live websites using Twitter Embedded Tweets and an additional 186,346 sites that used Twitter Embedded Tweets historically and 25,571 websites in the United States.
Get a list of 224,449 websites using Twitter Embedded Tweets which includes location information, hosting data, contact details, 247,297 currently live websites which includes 209,194 domains that redirect to sites in the list. 186,346 sites that used this technology previously and 25,571 websites in the United States currently using Twitter Embedded Tweets.