NSClient++ is a windows service that allows performance metrics to be gathered by Nagios (and possibly other monitoring tools). It is an attempt to create a NSClient and NRPE compatible but yet extendable performance service for windows.
This Nagios plugin allows to remotely monitor Windows hosts in a AGENTLESS fashion. Technically it is using the Win32 API from a Windows proxy server to the remote host. Syntax and feature wise it mirrors NSClient++ (CPU, RAM, Disk, Svc, Proc., etc)
Genma is a Nagios configuration file generator for Windows' systems that use the nsclient. It creates the host.cfg and services.cfg files. It is written in C# and requires .Net 2.0 or greater.