Originally a Unix-only tool, Nmap for Windows has been an important security resource for Windows shops for more than 10 years. This security scanner and network mapper can also be used to perform network inventory, manage service upgrade schedules, and monitor host or service uptime. It supports Windows 7, Windows Server 2008 and 2003, Windows Vista, and Windows XP SP1 and later.

Download: nmap.org/book/inst-windows.html

Zenmap is a cool tool for mapping a topology of devices connected to your network. This security scanner works off of , providing an interactive, animated visualization of hosts on a network, configured in rings. Click on a host and it moves to the center of your network topology, giving you the ability to easily trace the host's various connections. With Zenmap, information regarding potential vulnerabilities becomes that much easier to pinpoint, ensuring your firewalls and routers are working correctly.