Anubus is Nimbus, but just rolled forward to support the latest Azure Service Bus client. Since the Windows Service Bus, and it's client API, is only released when Windows Server is released, it lags far behind the Azure Service Bus and client API that is released much more often.
Anubus drops Windows Service Bus compatibility and embraces the latest Azure Service Bus.
Read more on the Anubus wiki
Nimbus is a .NET client library to add an easy to develop against experience against the Azure Service Bus brought to you by Damian Maclennan and Andrew Harcourt.
For more information go to The Nimbus website or the Documentation Wiki