Dbus is a good place to start. Raw sockets and shared memory are still necessary to get good enough performance in some cases. Dbus can be very slow! If something needs to happen several times per second, or big amounts of binary data should be transferred, dbus can become a bottleneck in embedded applications.

I think dbus works great for service discovery and for low-frequency low-bandwidth communication. For other cases, people just exchange a file descriptor over dbus and proceed to talk directly to each other.

dbus only covers a few use cases covered by all of these.

Things like signals, file locking and mmap are still pretty important. Even if your using dbus. (Eg use dbus to share a file and mmap it)