NServiceBus.Callbacks is an extension for NServiceBus to support defining callbacks on send operations. Callbacks can be used to map a response message to a stateful resource (e.g. an HTTP Request) without needing to use a message handler.
It is part of the Particular Service Platform, which includes NServiceBus and tools to build, monitor, and debug distributed systems.
See the Client-side callbacks documentation for more details on how to use it.
To test callbacks, install the testing package via NuGet:
Install-Package NServiceBus.Callbacks.Testing