When digging around for information about Apple's new Caching Server, I happened across this informative article about Caching Server for Mavericks by Dan Barrett. Definitely worth a read if you're interested in finding out how to make the most of your network connection with your Macs.
However, from there, I noticed a link to the Nagios plugins for OS X on github. The plugins contain a lot of useful functionality for monitoring OS X systems, and appear to support many versions, supposedly back to 10.4. They are all local scripts, so they need to run on the systems that you are checking.
There's a lot of useful stuff here.