Projects that expose information via JMX

Apache ActiveMQ - an open source Message Orientated Middleware platform which exposes its connection, destination and message statistics via JMX

Apache ServiceMix - an open source ESB based on JBI which exposes all of its component, endpoint and message exchange statistics via JMX

Hibernate - Exposes statistics via JMX

Spring Framework - Can register and expose Spring beans

Chires - An AOP-based project to dynamically instrument applications and expose them through JMX

commons-modeler - A framework for creating JMX MBeans. Allows for the storage of MBean metadata in seperate XML files.

glassbox inspector - Add JMX instrumenting to applications using AspectJ. There is a useful article on DeveloperWorks.