Enterprise Service Bus (ESB), .NET Service Bus, NServiceBus, RhinoServiceBus, MassTransit and so on. I'm trying to understand what each of these technologies have in common or not in common. I attended Juval Löwy's presentation on the .NET Service Bus earlier today and he stated that the .NET Service Bus could be used as a poor man's version of an ESB, so I would take that to mean that the .NET Service Bus is NOT an ESB, are any of the others a true ESB? If any of the others are a true ESB what would make them a true ESB as opposed to the .NET Service Bus?