Gitstalk is a Web app that allows you to sneak peek into the recent activities of other GitHub users. No Login, No BS. Just enter the username and you are good to fly!
The GitHub Matrix Screensaver for Mac OSX shows a constant stream of recent commits from GitHub.
Github Profile Visualizer is a tool for visualizing a developer based on their GitHub contributions, field of contributions and a lot more.
LanguageHealth is an easy way to compare programming languages based on how healthy they are over time. There are many tools out there for charting programming language popularity, but they tend to use metrics that I don't find very useful. LanguageHealth looks at the fraction of open-source commits to projects in a language.
GitHub Spray is a CLI to draw on your GitHub calendar heatmap
Through Alize, you can visualize your GitHub profile into the cool design page and use in your CV
DevFit takes advantage of Github data to generate visual and easy to understand reports of your contributions and allows to share them with the world.