htop - interactive process viewer
mytop - display MySQL server performance info like top
tcptrack - Monitor TCP connections on the network
trickle - user-space bandwidth shaper
monit - utility for monitoring services on a Unix system
rkhunter - run a system check for rootkits or other malware
apachetop - display real-time web server statistics
cronolog - write log messages to log files
rdiff-backup - local/remote mirror and incremental backup
pmap - report memory map of a process
multitail - browse through several files at once
ntop - display top network users
nmap - Network exploration tool and security / port scanner
netcat - TCP/IP swiss army knife
hping2 - send (almost) arbitrary TCP/IP packets to network hosts
lsof - list open files
ngrep - network grep
lynis - Security and system auditing tool
nagios - monitoring solutions for hosts, services, and networks
cacti - network graphing solution
nikto - Web Server and CGI Scanner
deny hosts - Script intended to help thwart SSH server attacks
My Traceroute - mtr combines the functionality of the ‘traceroute’ and ‘ping’ programs in a single network diagnostic tool.
Ettercap - a multipurpose sniffer/interceptor/logger for switched LAN
xjobs - It reads job descriptions line by line and executes them in parallel
Munin - is a networked resource monitoring tool that can help analyze resource trends and “what just happened to kill our performance?” problems
TCP dump - It Prints out a description of the contents of packets on a network interface that match the boolean expression.
mussh - MUltihost SSH