The Manage Jenkins >> System Information page provides detailed information about what is available on this Jenkins instance:
System Properties that can be used as arguments to the command line used to start Jenkins.
Environment Variables recognized on this system, with current values. This includes the environment variables defined by Jenkins and available on all systems as well as environment variables associated with plugins installed on this instance.
List of Plugins installed on the system.
Memory Usage gives a graph that shows the current memory usage for this instance.