Wikipedia
Launchd
In computing, launchd, a unified, open-source service-management framework, starts, stops and manages daemons, applications, processes, and scripts in Apple OS X environments. Dave Zarzycki at Apple designed and wrote launchd; Apple introduced it with Mac OS X Tiger and licenses it under the Apache License.
The launchd daemon essentially replaces:
Apple has stated that it intends to eliminate all of the aforementioned services in favor of launchd.
For Mac OS X v10.4 (Tiger) Apple moved most of the processes handled by the previously mentioned daemons to launchd.