VMware Server is a free virtualization product for Windows and Linux servers with enterprise-class support. It enables companies to partition a physical server into multiple virtual machines and to start experiencing the benefits of virtualization.
Zabbix offers great performance for data gathering and can be scaled to very large environments. Distributed monitoring options are available with the use of Zabbix proxies. Zabbix comes with a web-based interface, secure user authentication and a flexible user permission schema.