From Official zabbix site :
Zabbix is the ultimate enterprise-level software designed for real-time monitoring of millions of metrics collected from tens of thousands of servers, virtual machines and network devices. Zabbix is Open Source and comes at no cost.

SysGroup has written an OpenVMS agent for Zabbix.

The following platforms are supported: VAX, Alpha, Itanium.

Some platforms, especially VAX, do not have all the items.

For the Zabbix server, the version recommended is 3.4.x

Supported items