Search engines like Google scour the web to figure out how to rank content. But what if you want to know which of some 2000 technologies a web site is using? And, what if you want to know what the tech trends are across the 130 million largest sites on the web today? You could just dig through the source code for each site you’re interested in to answer these questions piecemeal, or you could repurpose other web site profilers designed for search engine optimization or other jobs.

Or, you could use BuiltWith. Built by one-man team Gary Brewer in Australia, looks at the publicly available code for each site, and figures out each piece of technology that it’s using. It shows that TechCrunch, for example, is using the WordPress VIP content management system, ad targeting from Quigo and AdSonar, traffic measurement from comScore, ChartBeat, Optimizely, Google Analytics, and many others. It also shows all the Javascript libraries and widgets that we’re using, including Facebook for Websites, JQuery, and the Twitter Platform.

By aggregating the data about usage across all of the sites that it tracks, BuiltWith can show which web technologies are gaining or losing in usage across the web. BuiltWith is monetizing all this publicly available but painful-to-aggregate data through a professional version called Trends Pro that lets people buy access to run custom reports across its database. Each report comes with further details on each included site, such as available contact information, and includes options to export to spreadsheets or into your company’s customer relationship manager software.