Veeam Monitor Free Edition

Veeam Monitor™ Free Edition is the free version of Veeam’s popular monitoring tool for VMware. With more than 35,000 installations worldwide, Veeam Monitor is the industry standard for VMware monitoring. It provides a comprehensive, performance-oriented view of your virtual infrastructure that you just can’t get with vCenter Server. And unlike some VMware monitors, Veeam Monitor doesn’t introduce its own monitoring framework, so it’s easy to deploy and maintain.

http://www.veeam.com/esxi-monitoring-free.html