management-agent.jar is the java agent that is used with the attach API to start the JMX agent in a target VM. It's the approach used in JDK 6 to start JMX in a running VM and predates the "jcmd ManagementAgent.start" command added in 7uX.

management-agent.jar will be problematic when we move to a modular JDK in JDK 9. This bug requests that this legacy mechanism be re-examined, the compatibility risk is probably not too high although tools such as VisualVM should be checked as it may be using this mechanism.