The Dgraph team is excited to make Ratel source available! The Ratel UI is the proprietary Dgraph data visualizer and cluster manager that powers the demo site https://play.dgraph.io. You can check out the Ratel source over on GitHub at https://github.com/dgraph-io/ratel.
Ratel is licensed under the Dgraph Community License and is not open source.
Any issues related to Ratel can be filed under the ratel repository.