git-cola: The highly caffeinated Git GUI
Full git and GitHub integration with Sublime Text
Typed interactions with the GitHub API v3
Some out-of-the-box hooks for pre-commit
Web application for posting, submitting, and evaluating assignments
Incremental merge for git
Git for Humans, Inspired by GitHub for Mac™
Version controlled file system
Walle 2.0 web
A Slack bot for GitHub organization management, and other things too