GitHub is an online collaboration site for developers and programmers. It is an online repository where multiple coders can commit software development changes.
Google Analytics is an extremely powerful data analytics tool for anyone who has a website. All it takes to set up is adding a small JavaScript in your webpage.
Google Webmaster Tools is a great search engine optimization (SEO) resource for any web developer who's goal is to analyze and drive more traffic to their site.
Gravatar, which stands for Globally Recognized Avatars, is an awesome free online service where anyone can create an account and upload an avatar image.