We're very impressed by the collective smarts of the security community and we highly recommend reading the whole list and investigating any tools you are unfamiliar with. Click any tool name for more details on that particular application, including the chance to read (and write) reviews. Many site elements are explained by tool tips if you hover your mouse over them. Enjoy!
ike-scan is a command-line tool that uses the IKE protocol to discover, fingerprint and test IPsec VPN servers. It scans IP addresses for VPN servers by sending a specially crafted IKE packet to each host within a network. Most hosts running IKE will respond, identifying their presence. The tool then remains silent and monitors retransmission packets. These retransmission responses are recorded, displayed and matched against a known set of VPN product fingerprints. ike-scan can VPNs from manufacturers including Checkpoint, Cisco, Microsoft, Nortel, and Watchguard.
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Latest release: version 1.9 on Jan. 24, 2007 (7 years, 9 months ago).
Amap is a great tool for determining what application is listening on a given port. Their database isn't as large as what Nmap uses for its version detection feature, but it is definitely worth trying for a 2nd opinion or if Nmap fails to detect a service. Amap even knows how to parse Nmap output files. This is yet another valuable tool from the great guys at THC.
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Latest release: version 5.4 on April 1, 2011 (3 years, 6 months ago).
NBTScan is a program for scanning IP networks for NetBIOS name information (similar to what the Windows nbtstat tool provides against single hosts). It sends a NetBIOS status query to each address in a supplied range and lists received information in human readable form. For each responded host it lists IP address, NetBIOS computer name, logged-in user name and MAC address. The original nbtscan was written by Alla Bezroutchko. Steve Friedl has written an alternate implementation.
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Latest release: version 1.5.1 on June 1, 2003 (11 years, 4 months ago).