How familiar are you with VMware? With this you can run preconfigured tools like in the above article to monitor your servers on most any platform.
If you want more information on built in tools within your operating system also let us know.
I have used BigBrother for Windows monitoring, Timbuktu and ARD (apple remote desktop) to monitor and push out updates to Mac’s on a network.
And of course good old VNC on any platform including LINUX, Ubuntu and the such.
Remember monitoring is not always legal and you should check before doing it!
For more information on VNC google VNC – it’s free as well! All of them are free except for ARD which is $500 for a site license.