Network Security Software

Nmap (Network Mapper) is a helpful ip scanner and network security utility. It uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. Once installed, simply use:

sudo nmap 192.168.1.*

for example to release its hounds to search out interesting IPs on that subnet. There are many other ways to use it, but this is a basic start. For full documentation type man nmap or search for nmap documentation on the web.