Some auctions demonstrate this pattern. Each bidder possesses a numbered paddle that is used to indicate a bid. The acceptance of the bid changes the bid price which is broadcast to all of the bidders in the form of a new bid. Chain of Responsibility passes a sender request along a chain of potential receivers. Command normally specifies a sender-receiver connection with a subclass.
Mediator has senders and receivers reference each other indirectly.
Observer defines a very decoupled interface that allows for multiple receivers to be configured at run-time. Mediator and Observer are competing patterns. We've found it easier to make reusable Observers and Subjects than to make reusable Mediators. On the other hand, Mediator can leverage Observer for dynamically registering colleagues and communicating with them.