D-Bus is a interprocess communication system via a message bus, a simple way for applications to talk to one another. For more information, see http://www.freedesktop.org/wiki/Software/dbus
There are currently two projects for providing DBus bindings for Tcl:
High level bindings:
"D-Bus Makes for Application Teamwork " (link broken on 2012-09-08) introduces D-Bus to a general audience.