Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.

Horangi - Horangi is a leading cyber-security solution that provides instant response and threat detection for companies who lack the time and expertise to monitor their system.

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.

Advanced IP Scanner - Advanced IP Scanner shows all network devices, gives you access to shared folders, and can even remotely switch computers off. Download it Free.

Acunetix - Audit your website security and web applications for SQL injection, Cross site scripting and other...