Amazon.com has started beta for a new "Simple Queue Service". It's a way to loosely couple web services, such that service A can post entries in the queue for other services to receive.

Personally, I think it's kind of primitive, at least as a synchronization tool, since apparently items can end up being read more than once, and there doesn't appear to be a way to atomically add an item to multiple queues. It's sure not competition for a JMS or MQ system. However, this probably won't stop it from becoming popular.