'Net Tools (2)', and 'Mrtg'

NET TOOLS (2)

153 net tools in one package. Cutting-edge security and network monitoring software for the Internet and Local Area Networks, providing clients with the ability and confidence to meet the challenges of tomorrow's technology. Net Tools is a very strong combination of network scanning, security, file, system, and administrator tools useful in diagnosing networks and monitoring your PC and computer's network connections for system administrators. Next to the essential core tools it includes a lot of extra valuable features. It’s a Swiss Army knife for everyone interested in a set of powerful network tools for everyday use. The size of Net Tools 4.5.74 is approximately 25 Mb.

http://users.pandora.be/ahmadi/nettools.htm

Mrtg

If you have a router and want to know what it does all day long, then MRTG is for you. It will monitor SNMP network devices and draw pretty pictures showing how much traffic has passed through each interface.

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