To find out what's running and get notified when services / hosts / servers / die you need http://www.nagios.org/about/ Nagios - an Open Source host, service and network monitoring program.

If you want to examine traffic on your network you need Wireshark http://www.wireshark.org/faq.html#q1.1 described as the world's most popular network protocol analyzer. It has a rich and powerful feature set and runs on most computing platforms including Windows, OS X, and Linux. Wireshark used to be known as Ethereal.

You can get lots of addins / graphing tools etc for nagios, probably can for wireshark, a keyword search on this site will show yo who else has commented on them. Both programs go back a long way and are actively developed.


You might also look at ntop http://www.ntop.org/overview.html I find it very helpful in seeing what is going on on the network. and http://www.zenoss.com/


look at these :


www.OpenNMS.org



www.zabbix.org



http://oss.oetiker.ch/mrtg/


http://sonic.net/wallwatcher/




www.adventnet.com/products/webnms/index.html