Acunetix - Audit your website security and web applications for SQL injection, Cross site scripting and other...
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
Shodan - Shodan is the world's first search engine for Internet-connected devices.
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use
Intruder - Intruder is a security monitoring platform for internet-facing systems.
Zenmap - Zenmap is the official cross-platform GUI for the Nmap Security Scanner.