osgregs/SEOstats
SEOstats is a powerful open source PHP class to get a lot of SEO relevant data such as detailed backlink analyses, keyword and traffic statistics, website trends, page authority, the Google Pagerank, the Alexa Trafficrank and much more. Therefore SEOstats gathers data from Google, Yahoo, SEOmoz, Alexa, Facebook and Twitter. SEOstats offers over 50 different methods to request SEO relevant data for websites.