title: What is an ESB and what is it good for?
body: <p>At a previous job, there was lots of talk about "Enterprise Service Bus" (ESB).  I read parts of a conceptual book about it, but never really understood how you would implement/integrate it in concrete terms.  I'm familiar with SOA/queueing/directory services/etc. but I don't understand what exactly an ESB is.</p>
  
  <p>Is it a concrete thing (service/server/broker/etc.) that you just hook all your apps up to it in different ways, or is it more just a conceptual way to design systems?</p>
  
  <p>Any explanations or links to good examples would be greatly appreciated.  Thanks.</p>