Public and private chat for GitHub. Gitter is built on top of GitHub, bringing unlimited public rooms and one-to-one chats to your repositories, with tight integration with your organisations, issues and activity. Unlike other chat services, Gitter is aimed specifically at developers, so includes features such as Markdown support with syntax highlighting, integrations with Trello, Jenkins, Travis CI, Heroku, BitBucket and loads more, and a flexible API and webhooks for custom integrations. They even offer a very generous free plan with unlimited public and private rooms.