Tornado is an open source version of the scalable, non-blocking web server and tools that power FriendFeed. The FriendFeed application is written using a web framework that looks a bit like web.py or Google's webapp, but with additional tools and optimizations to take advantage of the underlying non-blocking infrastructure.
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Wappalyzer is a browser extension that uncovers the technologies used on websites. It detects content management systems, eCommerce platforms, web servers, JavaScript frameworks, analytics tools and many more."
"Prototype takes the complexity out of client-side web programming. Built to solve real-world problems, it adds useful extensions to the browser scripting environment and provides elegant APIs around the clumsy interfaces of Ajax and the Document Object Model."
Hobo is an Open Source extension to Ruby on Rails which helps you build full blown web applications incredibly quickly and easily. Available as a Gem or Rails plugin, Hobo provides a simple, clean and elegant development framework which allows for rapid prototyping or production of the most sophisticated web applications.