Nmap is an open source tool designed for network exploration and security auditing. If you’ve ever had even a passing interest in networking, computer security, or how the Internet works, then you should check out this program. I’ve been using it at work a lot recently to do penetration testing. I must warn you, however, that you can get into deep shit if you use this for evil.

You can visit the Nmap website here. As an added bonus, they have links to more than a hundred other great network monitoring tools, white hat hacking utilities, and more! I got more than a dozen useful apps there today.