If you’re not completely new to the Internet, I’m sure you’ve browsed websites’ source codes many times. You can usually find out which CMS they’re using (WordPress is always obvious), find URLs of images the owners don’t want you to see and other fun stuff.
But source code also shows a bunch of other stuff – if you have Google Analytics installed, you can search for unique code UA-XXXXXX and learn which websites belong to one owner. You can do the same with AdSense code, default Piwik code and anything else that leaves a footprint.
I haven’t known of an easy tool that searches through source code throughout the internet but yesterday my coworker showed me one – NerdyData.
It’s a paid tool but they have a free option which should easily cover a few projects.
Beside searching for Google Analytics, Optimizely, Google AdSense, Visual Website Optimizer, you can also search for meta keywords, meta description and whatever else you find interesting.
The one issue I found was that the data is not refreshed regularly so you might find broken links and non-existing websites.
All in all a great tool, so go and check what your competitor also owns. 😉