p0f
passive OS fingerprint utility
DNSenum
dns enumerator. gathers general info, NS, MX, bind version
snmpwalk, snmpcheck
snmp auditing tool
fierce
smtp-user-enum
scapy
dmitry
nping
part of Nmap suite
nmap
amap
Maltego/Casefile
Nessus
OpenVAS
Armitage
Ettercap
John the Ripper
Wifi auditing
Gerix