Sourcegraph for GitHub - Browse and search GitHub like an IDE
Codeology - Open-source algorithm that visualizes GitHub projects
GitHub Reviews - A place for reviews of popular open source projects
GitHub Visualizer - Enter user/repo and see the project visually
Gource - Gource is a software version control visualization tool.
Sourcegraph - Sourcegraph is a free, self-hosted code search and intelligence server that helps developers find, review, understand, and debug code. Use it with any Git code host for teams from 1 to 10,000+.