http://www.centreon.com/ ..or install via FAN: http://www.fullyautomatednagios.org/wordpress/
Makes life so much better.
Nagios, and a host of other popular software that's difficult to use, exist because the alternatives are so poor.
We use it for a small ISP since nearly two years and are quite happy with it. All limitations that came up during integration could be fixed by writing some small scripts. Even upgrades worked.. :)
So if you have any Zabbix pain that might be waiting for us, please share.
They do offer an API that is quite usable. I've build a simplified interface for our less trained staff members with it.
You won't find any RRD files which might be a problem for you. Until now that was only a theoretical problem for us.
Shinken was written by Jean Gabès as a proof of concept for a new Nagios architecture. Believing the new implementation was faster and more flexible than the old C code, he proposed it as the new development branch of Nagios 4.[3] This proposal was turned down by the Nagios authors, so Shinken became an independent network monitoring software application compatible with Nagios