Microsoft BizTalk Server vs Azure AppFabric Service Bus...?
BizTalk Server is not a 'bus', it's a 'broker'. The word 'bus' indicates a subsystem that transfers data between components. You might say that BTS does exactly that, but it does it by sitting in the middle of a hub and spoke model, distributing messages to appropriate receivers. Since it often plays a very active role in the distribution of messages, the broker label is more appropriate.
This basically also gives you a pretty good idea about the differences between the Azure Service Bus and BTS. The Azure Service Bus is basically just a data transfer subsystem that enables you to connect various endpoints together across network topology barriers (it enable you to use callback channels to invoke services behind firewalls).
BTS, on the other hand, doesn't do that. Instead, it has these Message Broker features:
- Orchestration
- Message translation
- Content-based routing
- Durable messaging
- Business Analytics Monitoring
- Operations support/diagnostics
- probably some more I forget right now :)
BTS and the Azure Service Bus are really two entirely different things, and might be used complementarily. For example, it's easy to conceive of connecting two BizTalk Servers via the Azure Service Bus.
The BizTalk and AppFabric Service Bus teams at Microsoft are actually tightly collaborating and we (I work there) are integrating BizTalk's capabilities with AppFabric and Service Bus over time. For BizTalk we have Windows Azure AppFabric Connect - which lets you plug BizTalk into Service Bus. At PDC'10 we announced (http://bit.ly/9gm2zI) that we'll be bringing a subset of the BizTalk integration features into Service Bus - you'll be hearing a lot more about the extent of those capabilities over the course of the current year.
For now, think of the products as highly complementary.
I hope that helps.
There is a new feature coming to Azure AppFabric sometime this year simply called "Integration" which basically enables Biztalk services on Azure.
http://www.microsoft.com/windowsazure/appfabric/overview/default.aspx#top