OS X: Is there a built-in scheduler program?
While KeithB's answer is correct, actually, cron is being deprecated in favor of the OS X specific launchd.

Commands to be run via launchd are described in Apple "plists", or property lists, which are really just XML files:

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
"http://www.apple.
com/DTDs/PropertyList-1.0.dtd"&gt;
&lt;plist version="1.0"&gt;
&lt;dict&gt;  
    &lt;key&gt;Label&lt;/key&gt;
    &lt;string&gt;com.apple.periodic-daily&lt;/string&gt;
    &lt;key&gt;ProgramArguments&lt;/key&gt;
    &lt;array&gt; 
        &lt;string&gt;/usr/sbin/periodic&lt;/string&gt;
        &lt;string&gt;daily&lt;/string&gt;
    &lt;/array&gt;
    &lt;key&gt;LowPriorityIO&lt;/key&gt;
    &lt;true/&gt;
    &lt;key&gt;Nice&lt;/key&gt;
    &lt;integer&gt;1&lt;/integer&gt;
    &lt;key&gt;StartCalendarInterval&lt;/key&gt;
    &lt;dict&gt;  
        &lt;key&gt;Hour&lt;/key&gt;
        &lt;integer&gt;3&lt;/integer&gt;
        &lt;key&gt;Minute&lt;/key&gt;
        &lt;integer&gt;15&lt;/integer&gt;
    &lt;/dict&gt;
&lt;/dict&gt;
&lt;/plist&gt;


Having said that, it's not a very user friendly (nor Mac-like) way of scheduling commands to be run. This question on SuperUser lists a few GUI alternatives, including:


Lingon (http://sourceforge.net/projects/lingon/) (Free, may not work on 10.6)
Lingon (http://www.peterborgapps.com/lingon/) (Not free, works on 10.6)




launchd Editor ($5 Shareware)