ZenPacks.community.Varnish is a project mainly written in Python, it's free.
ZenPack to monitor Varnish
This ZenPack adds a template to Zenoss to monitor a Varnish server.
In order to use this package you need first setup a cronjob in the target machine to export the results of varnishstat:
*/2 * * * * /<path_to_varnish>/bin/varnishstat -1 > /var/www/status/varnish.txt
The above example will generate a varnish.txt file containing the stats every 2 minutes.
This file must be accessible through the web in order to our pack access it.