Nikto is an Open Source (GPL) web server scanner which performs comprehensive tests against web servers for multiple items, including over 3500 potentially dangerous files/CGIs,
free open source location tracker for laptops - only the owner can track its location. Mac users can even get pictures of their thieves with the iSight camera!
DenyHosts is a script intended to be run by Linux system administrators to help thwart SSH server attacks (also known as dictionary based attacks and brute force attacks).