Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
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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.
Cybrary - Free courses in cyber security
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use
CYREX - Web security vulnerability assessment & penetration testing