The Simpleweb - SNMP / Network Management Software

Cacti	Ian Berry	RRD Front-end
Cfengine	Oslo University College	Unix configuration management and anomaly detection software. Widely used.
Flowtools	Mark Fullmer	Software for collecting and processing NetFlow data
Fprobe	Fprobe team	NetFlow probe
libsmi	TU Braunschweig	A library to access SMI MIB information
Nagios	OpenSource	Host and service monitor.
net-snmp	Univ of California, Davis	Various tools relating to the Simple Network Management Protocol
NfSen	NfSen team	Graphical front end for nfdump
nmap	Nmap team	A utility for network exploration or security auditing
ntop	Luca Deri	A tool that shows the network usage, similar to what the popular 'top' Unix command does.
RRDtool	Tobias Oetiker	RRDtool as a reimplementation of MRTGs graphing and logging features.
scli	IUB	Scli addresses the need for small and efficient command line utilities to monitor and configure systems.
Wireshark	Gerald Combs	Wireshark is a network protocol analyzer for Unix.