qmail-monitor is a patch to qmail that offers mail monitoring (duplication) functionality on both incoming and outgoing SMTP traffic. the monitor ruleset is intuitive and allows the administrator to make changes without restarting the server processes.
OpenDDS is a C++ implementation of the Object
Management Group's Data Distribution Service for
real-time systems specification. In particular,
this implements the Data-Centric Publish-Subscribe
(DCPS) layer of the DDS specification.