Really Simple Discovery is a way to help client software find the services needed to read, edit, or "work with" weblogging software.
https://cyber.law.harvard.edu/blogs/gems/tech/rsd.html
Syndication Techniques
Get access to data on 62,743,148 websites that are Really Simple Discovery Customers. We know of 29,013,717 live websites using Really Simple Discovery and an additional 33,729,431 sites that used Really Simple Discovery historically and 3,232,198 websites in the United States.
Get a list of 62,743,148 websites using Really Simple Discovery which includes location information, hosting data, contact details, 29,013,717 currently live websites and an additional 2,208,651 domains that redirect to sites in this list. 33,729,431 sites that used this technology previouslyand 3,232,198 websites in the United States currently using Really Simple Discovery.
Countries
Financial
Group
Region