Daemons have become pretty confusing on Mac OS X. Originally these were handled by
inetd, then xinetd, and now launchd has taken over. Unfortunately, there's
a mess of left over stuff hanging around: you'll still find services in /etc/xinet.d and
No longer true as of Snow Leopard. You don't have an xinetd.d directory and although you may still have leftover rc.common and rc.netboot files, they are bnot used. Launchd has taken over.
The goal of launchd is to replace xinetd, cron, and anything you might have stuck
in rc.local or StartupItems. It controls system programs, but it can be used
for ordinary user processes also.
Anything you want controlled by launchd needs a plist file describing what to do if
you want it to start automatically, but you can use it to daemonize a specific command also:
$ launchd -d -- ~/bin/ltest
However, by using configuration files, you can use "launchctl" to more powerfully
control your jobs. There's an interactive mode - if you just type "launchctl" you
can then control daemons from its shell: