- nessus http://www.nessus.org
- nagios http://www.nagios.org
- cacti http://www.cacti.net
- wireshark http://www.wireshark.org
- zenoss http://www.zenoss.com
Commands
- top
- atop http://freshmeat.net/projects/atop/
- ntop http://www.ntop.org/
- vmstat, free
- w, uptime
- ps, pmap
- iostat
- sar
- netstat
- tcpdump (see wireshark for GUI)
- nmap
