Angry IP Scanner
Angry IP Scanner is a free open source network security application developed by Anton Keks for Linux, Macintosh, and Windows. It is a tool to help network administrators find vulnerabilities and bottlenecks in their networks. The program works by sending pings of various protocols to the range of IP addresses you specify and finding which addresses respond to the various pings which helps the administrator to determine which computers may be at risk. The program has been around since at least 2006.
I found this program will looking for a program to determine the security of my computer when I was living in an apartment with hundreds of wired and wireless networks around me.