This toolkit makes use of the Secure Sockets Layer and Transport Layer Security protocols, as well as the SSLeay cryptography library. It's certified to meet FIPS-140 standards, and widely used by large organizations and commercial software providers. (OS independent)
This implementation of Secure Shell (SSH) technology allows administrators to operate a remote host using a public key. Developed by the OpenBSD project, OpenSSH encrypts all traffic, including passwords, in order to protect it from hackers and identity thieves. It's integrated into most Linux distributions and Mac OS X, and versions are also available for Windows, Unix, Solaris, and others.
Short for "network mapper," Nmap scans network ports and returns information about which hardware is connected to the network, operating systems, and application versions. It supports all major operating systems, including Windows, Linux, Unix, Mac OS X, and others.
9. Ossec HIDS
This host-based intrusion detection system (HIDS) has recently been gaining popularity among enterprise users, in part because of its high scalability. If an attack overcomes your network defenses, Ossec HIDS stops the attack at the host level, and it can be configured to notify the network administrator when an attack occurs. It's compatible with many firewalls and all the major operating systems.
Wireshark titles itself "the world's most popular network protocol analyzer." Formerly known as "Ethereal," Wireshark allows the user to see all traffic being passed over an Ethernet network. It runs on Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and others.