Packages 
Package Description
org.apache.activemq.advisory  
org.apache.activemq.broker
The core classes for the ActiveMQ Message Broker and its connectors.
org.apache.activemq.broker.cluster  
org.apache.activemq.broker.inteceptor
MessageInteceptor malarky
org.apache.activemq.broker.jmx
JMX MBeans for the broker and its core connectors.
org.apache.activemq.broker.region
Region abstraction and implementations in the Broker.
org.apache.activemq.broker.region.cursors
Cursors used to page persistent messages into the broker from the store
org.apache.activemq.broker.region.group
Classes to implement the Message Groups feature.
org.apache.activemq.broker.region.policy
The policies which can be associated with a particular destination or wildcard.
org.apache.activemq.broker.region.virtual
Implementation classes for Virtual Destinations
org.apache.activemq.broker.scheduler
The Message Scheduler for delayed (or scheduled) message delivery
org.apache.activemq.broker.scheduler.memory  
org.apache.activemq.broker.util
Some utility Broker Plugins
org.apache.activemq.broker.view
Broker Plugins for visualising the current system
org.apache.activemq.filter  
org.apache.activemq.memory  
org.apache.activemq.memory.buffer  
org.apache.activemq.memory.list  
org.apache.activemq.network
Support for federated networks of brokers.
org.apache.activemq.network.jms
Support for a federated network using a foreign JMS provider.
org.apache.activemq.plugin  
org.apache.activemq.proxy  
org.apache.activemq.security
Plugable Security Adapter framework along with default implementations such as the JAAS implementation.
org.apache.activemq.store
The APIs which need to be implemented for persistent message stores for durable messaging
org.apache.activemq.store.memory
VM based implementation of message persistence
org.apache.activemq.transaction  
org.apache.activemq.transport  
org.apache.activemq.transport.auto  
org.apache.activemq.transport.auto.nio  
org.apache.activemq.transport.logwriters  
org.apache.activemq.transport.nio  
org.apache.activemq.transport.peer
Peer based Transport implementation which does not require central servers to connect to
org.apache.activemq.transport.protocol  
org.apache.activemq.transport.vm
In-JVM based Transport implementation.
org.apache.activemq.usage  
org.apache.activemq.util  
org.apache.activemq.util.osgi