Armory
Whoisup
WhoisUP monitors hosts via ICMP and shows the status in a web page. When a host is down, the script can send mail, syslog message, open a popup message or play a sound. The script uses NMap to send ICMP packets and to save the host status into an XML ...
VirtualBox
VirtualBox is a powerful x86 and AMD64/Intel64 virtualization product for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software under the terms of the ...
Netdisco 
(1 rating)
Netdisco is an Open Source web-based network management tool first released publically in 2003. The target users are large corporate and university networks administrators. Data is collected into a Postgres database using SNMP and presented with a clean web interface using Mason. Configuration information and connection data for network devices ...
Ostinato (1 rating)
Ostinato is an open-source network packet and traffic generator and analyzer with a friendly GUI. It aims to be "Wireshark in Reverse" and become complementary to Wireshark. It features custom packet crafting with editing of any field for several protocols: Ethernet, 802.3, LLC SNAP, VLAN (with Q-in-Q), ARP, IPv4, IPv6, ...
Observium (1 rating)
Observium is an auto-discovering PHP/MySQL based network monitoring system focused primarily on Cisco and Linux networks but includes support for a wide range of network hardware and operating systems. Observium has grown out of a lack of easy to use NMSes. It is intended to provide a more navigable interface ...
Overlook - Fing
Fing is the ultimate tool for network discovery and scanning, allowing administrators to troubleshoot their network easily and at the speed of light. Once installed on a Windows, Mac or Linux computer, your home, office and corporate network are just one click away.
Likewise Software
Securely Integrate Linux, Unix, and Mac with Active Directory by allowing the machines to join the domain and users to authenticate with their domain credentials.
KeePass (4 ratings)
KeePass is a free open source password manager, which helps you to manage your passwords in a secure way.
Wireshark 
(17 ratings)
Wireshark is the world's foremost network protocol analyzer, and is the de facto (and often de jure) standard across many industries and educational institutions.
netcat (4 ratings)
Netcat is a featured networking utility which reads and writes data across network connections, using the TCP/IP protocol. It is designed to be a reliable "back-end" tool that can be used directly or easily driven by other programs and scripts. At the same time, it is a feature-rich network debugging ...
Nessus (3 ratings)
The Nessus vulnerability scanner, is the world-leader in active scanners, featuring high speed discovery, configuration auditing, asset profiling, sensitive data discovery and vulnerability analysis of your security posture. Nessus scanners can be distributed throughout an entire enterprise, inside DMZs, and across physically separate networks. When Nessus is managed with Tenable's ...
Snort (1 rating)
Snort is an open source network intrusion prevention and detection system utilizing a rule-driven language, which combines the benefits of signature, protocol and anomaly based inspection methods. With millions of downloads to date, Snort is the most widely deployed intrusion detection and prevention technology worldwide and has become the de ...
Metasploit Framework (3 ratings)
The Metasploit Framework is a development platform for creating security tools and exploits. The framework is used by network security professionals to perform penetration tests, system administrators to verify patch installations, product vendors to perform regression testing, and security researchers world-wide. The framework is written in the Ruby programming language ...
hping (1 rating)
hping is a command-line oriented TCP/IP packet assembler/analyzer. The interface is inspired to the ping(8) unix command, but hping isn't only able to send ICMP echo requests. It supports TCP, UDP, ICMP and RAW-IP protocols, has a traceroute mode, the ability to send files between a covered channel, and many ...
Kismet (1 rating)
Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system. Kismet will work with any wireless card which supports raw monitoring (rfmon) mode, and can sniff 802.11b, 802.11a, and 802.11g traffic. Kismet identifies networks by passively collecting packets and detecting standard named networks, detecting (and given time, ...
iperf (1 rating)
Iperf was developed by NLANR/DAST as a modern alternative for measuring maximum TCP and UDP bandwidth performance. Iperf allows the tuning of various parameters and UDP characteristics. Iperf reports bandwidth, delay jitter, datagram loss.
tcpdump (1 rating)
A command-line packet sniffer capable of dumping varying amounts of detail per packet to stdout, in real time. Originally written for UNIX-like systems, a port for Microsoft Windows was created and named WinDump.
John the Ripper (1 rating)
John the Ripper is a fast password cracker, currently available for many flavors of Unix (11 are officially supported, not counting different architectures), Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. Besides several crypt(3) password hash types most commonly found on various Unix flavors, ...
ettercap
Ettercap is a suite for man in the middle attacks on LAN. It features sniffing of live connections, content filtering on the fly and many other interesting tricks. It supports active and passive dissection of many protocols (even ciphered ones) and includes many feature for network and host analysis.
Nikto
Nikto is an Open Source (GPL) web server scanner which performs comprehensive tests against web servers for multiple items, including over 3500 potentially dangerous files/CGIs, versions on over 900 servers, and version specific problems on over 250 servers. Scan items and plugins are frequently updated and can be automatically updated ...
OpenSSH (1 rating)
OpenSSH is a FREE version of the SSH connectivity tools that technical users of the Internet rely on. Users of telnet, rlogin, and ftp may not realize that their password is transmitted across the Internet unencrypted, but it is. OpenSSH encrypts all traffic (including passwords) to effectively eliminate eavesdropping, connection ...
PuTTY (12 ratings)
PuTTY is a free implementation of Telnet and SSH for Win32 and Unix platforms, along with an xterm terminal emulator. It is written and maintained primarily by Simon Tatham.
THC-Hydra
A very fast network logon cracker which support many different services. Currently this tool supports: TELNET, FTP, HTTP, HTTPS, HTTP-PROXY, SMB, SMBNT, MS-SQL, MYSQL, REXEC, RSH, RLOGIN, CVS, SNMP, SMTP-AUTH, SOCKS5, VNC, POP3, IMAP, NNTP, PCNFS, ICQ, SAP/R3, LDAP2, LDAP3, Postgres, Teamspeak, Cisco auth, Cisco enable, LDAP2, Cisco AAA (incorporated ...
ShowIP (1 rating)
Firefox plugin by Jan Dittmer. Shows the IP address of the current page in the status bar. It also allows querying custom services by IP (right mouse button) and Hostname (left mouse button), like whois, netcraft. Additionally you can copy the IP address to the clipboard. This extension was formerly ...
Tamper Data (1 rating)
Firefox plugin by Adam Judson. Use Tamper Data to view and modify HTTP/HTTPS headers and post parameters, trace and time http response/requests, and security test web applications by modifying POST parameters.
dsniff
dsniff is a collection of tools for network auditing and penetration testing. dsniff, filesnarf, mailsnarf, msgsnarf, urlsnarf, and webspy passively monitor a network for interesting data (passwords, e-mail, files, etc.). arpspoof, dnsspoof, and macof facilitate the interception of network traffic normally unavailable to an attacker (e.g, due to layer-2 switching). ...
THC-Amap
Amap is a next-generation tool for assisting network penetration testing. It performs fast and reliable application protocol detection, independent on the TCP/UDP port they are being bound to.
aircrack (1 rating)
aircrack is an 802.11 WEP and WPA-PSK key cracking program that can recover keys once enough data packets have been captured. It implements the standard FMS attack along with some optimizations like KoreK attacks, thus making the attack much faster compared to other WEP cracking tools. In fact, aircrack is ...
wget (1 rating)
GNU Wget is a free software package for retrieving files using HTTP, HTTPS and FTP, the most widely-used Internet protocols. It is a non-interactive commandline tool, so it may easily be called from scripts, cron jobs, terminals without X-Windows support, etc. GNU Wget has many features to make retrieving large ...
Ophcrack
Ophcrack is a Windows password cracker based on rainbow tables. It is a very efficient implementation of rainbow tables done by the inventors of the method. It comes with a GTK+ Graphical User Interface and runs on Windows, Mac OS X (Intel CPU) as well as on Linux. Cracks LM ...