LibWhisker is a Perl library for vulnerability scanning and exploitation. It can create custom HTTP packets, which can be used to counteract intrusion detection systems.
LibWhisker is not a standalone tool, it is simply a library for HTTP packet creation.
Nikto is a scanning tool for webserver vulnerabilities. It includes many attack vectors and is designed to test a webserver quickly and thoroughly for known vulnerabilities.
Being designed for speed, Nikto is visible to httpd admins via log traces, however it does include support for the anti intrusion detection system LibWhisker.
dSniff includes packet sniffing and traffic analysis tools. dSniff can do things like decode passwords being sent over a network and display them in plain text, intercept SSH sessions, and spy on web traffic.
It can also spy on AIM, and break some ethernet switches.