w3af - w3af is a Web Application Attack and Audit Framework
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
Nikto - Nikto is an Open Source (GPL) web server scanner which performs comprehensive tests against web...
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use
Nessus - Nessus Professional is a security platform designed for businesses who want to protect the security of themselves, their clients, and their customers.
Zenmap - Zenmap is the official cross-platform GUI for the Nmap Security Scanner.