Unity Collaborate is a simple way for small teams to save, share, and sync their Unity project. It’s cloud-hosted and easy to use, so your entire team can contribute to the Project, regardless of location or role.
Collaborate is currently in closed Beta, and available to select teams who are actively developing a Unity project. Sign up at http://developer.cloud.unity3d.com/collaborate.
Is something described here not working as you expect it to? It might be a Known Issue. Please check with the Issue Tracker at issuetracker.unity3d.com.