currently i've got 5 servers (3 with windows server and 2 with linux). I am looking for a tool to monitor all the 5 servers from a windows machine (not the linux one, as i'd be using Nagios). I mean, i want to monitor all the 5 servers from one of the 3 Windows Machines, and i wonder if there exists any software for doing that. Thanks a lot!
You could try spiceworks.
Nagios also offers a windows client. Are you just not interested in using it for both Linux and Windows?
I suggest you to go with Nagios as it is the best Monitoring system till now I have heard. you can monitor both Linux and Windows server
There are quite a few packages out there that do this. We're using Intermapper from Dartware, which runs on Windows. It's a non-free package, but it is plenty sophisticated for what we're doing. Like Nagios you can create custom probes using any scripting language Windows supports (we're using Perl, but we could just as easily do PowerShell), and even compiled utilities if you'd rather go that route.
I like argent guardian (not free). You might take a look at polymon (free and which claims SNMP support- I've never used the SNMP portion) I know you can add the /n software (also not free but well worth the price for what you get) get-snmp cmdlet and get the data that way so perhaps a combination of /n software and polymon.
You may want to look at a SAAS solution that allows you to access your data from any browser. Sources of info from Linux and Windows. Check out AppFirst and Scout.
What about a SaaS solution like AlertSite or AlertFox? Some of them have also free options, e. g. http://www.alertfox.com/free-website-monitoring/