Wappalyzer

Wappalyzer is a simple Mozilla Firefox complement that tells you which technology each website uses.

It's really easy to use. After installing it, you'll see small icons in the lower right hand corner of your browser. Just hover your mouse over them to find out whether that website is using Google Analytics, jQuery, Wordpress, Quantcast, etc.

Wappalyzer is the perfect tool for programmers and website administrators. It'll help you figure out what each website is running in the background.