Gitter is an open-source instant messaging and chat room system written in JavaScript. It is similar to Slack, but designed for individuals (specifically developers and GitHub users) instead of businesses. For an example, you don't need to create an account for Gitter -- you can simply login with your Twitter or GitHub account. Individual chat rooms can also be created for individual git repositories on GitHub. The free option allows for the creation of a single private chat room, with all basic features enabled, while the paid subscription allows for the creation of multiple chat rooms.