NServiceBus.UniformSession provides a uniform API for accessing messaging operations in library code, similar to IBus in NServiceBus 5 and lower. It works whether or not the current code is in a message handler context with an IMessageHandlerContext or outside a message handler context with an IMessageSession.
It is part of the Particular Service Platform, which includes NServiceBus and tools to build, monitor, and debug distributed systems.
See the Uniform Session documentation for more details on how to use it.