The CORBA COS Notification Service (as specified by the OMG - www.omg.org) is a publish/subscribe messaging service built on top of CORBA, and is an OMG standard Common Object Service (COS). It has a rich API for exploring and managing the flow of notification events inside, and between, services. For a good Open Source example implementation of the COS Notification Service specification, see omniNotify at http://sourceforge.net/projects/omninotify
cossak (Common Object Services Swedish Army Knife) is a graphical tool that uses the COS Notification Service API to allow developers and system administrators to browse and manipulate the EventChannelFactory, EventChannel, Admin, Proxy, and Filter objects. As far as I know, there are no other Open Source tools for either browsing or manipulating COS Notification Service daemons.
Some of cossak's operations include: get and set QoSProperties, federate channels, disconnect consumers and suppliers (including breaking federation), observe traffic passing through FilterAdmin objects, add and remove filters, and create new channels.
Browsing (and light manipulation of) the COS Naming Service is also supported, mostly to facilitate working with COS Notification Service daemons. Some of the operations that cossak can perform against a Naming Service include: object references can be removed, browsed COS Notification Service objects can be registered, and objects in the Naming Service can be 'pinged' to make sure that they are still active.
cossak uses the free (and Open Source) version of the JGraph component (www.jgraph.com) for the visual display of the component objects in the COS Notification Service. JGraph is licensed under the LGPL, and while the end-user is required to have the JGraph JAR installed on their machine, the code for JGraph is external to this project.