Patch Bay is the JMS implementation provided within ATG which simplifies the process of creating JMS applications. Patch Bay includes an API for creating the Nucleus components which can send and receive messages, and a configuration file where you can declare these components and your JMS destinations. There are various features and events in ATG which makes use of JMS and uses Patch Bay. E.g. registration, login/logout events, scenarios, various commerce actions etc.
Refer to the following documentation for more details about Patch Bay: