The KDE project today removed the inter-application communication system DCOP from the head of its Subversion repository; it is being replaced by FreeDesktop's D-BUS. Thiago Macieira explains:
D-BUS brings us better interoperability with many other programs. While DCOP was pretty much restricted to KDE applications (yes, I know there were C bindings, but not many people used it...), D-BUS already comes with bindings for several other major frameworks: glib, Java, Python, Perl, Mono, etc. D-BUS has been designed from the ground up to be an interoperable IPC system and also to replace DCOP when the time came. And so it did.
D-BUS also allows us to better talk to our own system: projects like HAL and Avahi are already being used by many Linux distributions to let normal applications get access to some privileged resources. In time, I also hope the Portland Project to come around and use D-BUS for its IPC needs, thus freeing us from using a special library with its own protocol to do what D-BUS already does.