As primary a Windows admin I get a bit discouraged by products like Nagios – although it’s definitely a cool product installing it seem complex and with little knowledge on Linux maintaining it even more so.

So are there any Windows (free) alternatives out there?

Yes, and propably more than one, however is there any open source/free versions among these?

I found two;

OpenNMS

http://opennms.org/wiki/Installation:Windows

It claim to run on windows and have basic capabilities, I have not looked into details so I can’t say just how deep it goes (Nagius supports SNMP and very detailed monitoring, OpenNMS at a glance seem more like superficial monitoring).  Anyway, it’s free and may just be enough for you, so take a look at it.

Demo available at;
http://demo.opennms.org/opennms/index.jsp
user and password is both “demo”

SpiceWorks

http://www.spiceworks.com

I actually tested this once (a previous version), it is quite fine for smaller sites (and seem more extensive than OpenNMS), but when it come to wan connected sites it seem a bit heavy (works without agents installed).  Then again, it’s free and this one is quite easy to setup and manage.

Yet other alternatives (Non windows though) is;
http://www.zenoss.com/
http://www.zabbix.com/

And this one that seem commercial;
http://www.groundworkopensource.com/