p0f
P0f is a tool that utilizes an array of sophisticated, purely passive traffic fingerprinting mechanisms to identify the players behind any incidental TCP/IP communications (often as little as a single normal SYN) without interfering in any way.
smtp-user-enum
smtp-user-enum is a tool for enumerating OS-level user accounts on Solaris via the SMTP service (sendmail). Enumeration is performed by inspecting the responses to VRFY, EXPN and RCPT TO commands. It could be adapted to work against other vulnerable SMTP daemons, but this hasn’t been done as of v1.0.
snmp-check
Like to snmpwalk, snmpcheck allows you to enumerate the SNMP devices and places the output in a very human readable friendly format. It could be useful for penetration testing or systems monitoring. Distributed under GPL license and based on "Athena-2k" script by jshaw.
SSLyze
SSLyze is a Python tool that can analyze the SSL configuration of a server by connecting to it. It is designed to be fast and comprehensive, and should help organizations and testers identify misconfigurations affecting their SSL servers.
theHarvester
The objective of this program is to gather emails, subdomains, hosts, employee names, open ports and banners from different public sources like search engines, PGP key servers and SHODAN computer database.