How to execute a Folder Action or another Automator script when I make changes to a folder?
Using launchd, you could save a property list like this in ~/Library/LaunchAgents/ and load it with something like launchctl load ~/Library/LaunchAgents/automator_test.plist or by logging out and back in.

&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;automator_test&lt;/string&gt;
    &lt;key&gt;ProgramArguments&lt;/key&gt;
    &lt;array&gt;     
        &lt;string&gt;automator&lt;/string&gt;
        &lt;string&gt;/Users/username/Desktop/Test.workflow&lt;/string&gt;
    &lt;/array&gt;
    &lt;key&gt;WatchPaths&lt;/key&gt;
    &lt;array&gt;
        &lt;string&gt;/Users/username/Desktop/&lt;/string&gt;
    &lt;/array&gt;
    &lt;key&gt;StartInterval&lt;/key&gt;
    &lt;integer&gt;0&lt;/integer&gt; &lt;!-- run at most every 0 seconds, by default 10 --&gt;
&lt;/dict&gt;
&lt;/plist&gt;


Launchd only detects changes to files when they are saved atomically (or deleted and recreated every time they are saved). Most OS X apps perform atomic saves, but for example TextMate and vim don't.