Messaging… 

has queue

Idempotency - can handle multiple copies of the same message might use ID to ignore dup messages. Or work may be inherently idempotent (e.g. resizing image)

Messaging systems MSMQ; Azure queues; 

DTC - used with MSMQ to allow for tying the removal of message from queue with the work done against a database.

Use case for James to use messaging: reporting; large amounts of information; expensive work offline;

Mass Transit / NServiceBus on MSMQ

Book: Enterprise Integration Patterns - ? Wolf

Mongo DB as a queue

Where is messaging appropriate

Queue is distinct from messaging.

Long poll on HTTP/Rest