Vehicle Detection Using Magenetic Sensors
I developed an application for using two sensor nodes (not including the base station) to detect the vehicles on the road. (some real-road traces are also included in this zip file)
Nessus
Nessus is a very good vulnerability scanner, and is free. It can detect the OS type, hosting services, and vulnerabilities. A drawback is the vulnerability knowledge (script) will be late for seven days if it's free version. Currently (2007) its server side software cannot run on Windows, but it provide a Windows client, which is easy to use.
Here is an example report of a scan session. It takes less than one hour to scan a C class network.