Realm Object Server, developer edition has been sunset and support for this version is ending April 30th, 2018.
Please see the official announcement.
Instead a Cloud version is available free to try here: cloud.realm.io.
Realm Object Server
Realm Object Server provides synchronization of Realms between devices and provides authentication and access control services.
To get started, you'll want to follow our installation documentation that can be found here
To manage and edit users and data synced to the Realm Object Server, use Realm Studio. It's available free for macOS, Windows, and Linux. Download it here.
Learn how to start programming with Realm
Learn how to manage and customize your self-hosted instance
For more information on Realm, visit realm.io.