With a simple modification to change the path to the config.inc.php file, you can use this http://modx.com/extras/package/bkupmodx,
It's a stand-alone backup package, with a fairly simple config file. A few hints.
Edit the model_config.class.php file on line 36 to point to your core/config/config.inc.php file. The most elegant method would be to get the root config.core.php file and use that for the path to the core and the name of the config.inc.php file, in case those have been changed. The simplest way would be to just hard-code the path.
Either move the backup's config.inc.php file outside of the web root and change the path in a couple of files, or use web server access rules to prevent access to it.
[ed. note: sottwell last edited this post 6 years, 8 months ago.]