For the IPad. Not sure how long this will be free for. Normally $10.49.
"Net Master is the ultimate mobile solution for all your network analysis and diagnostic problems. Net Master is a utility application developed for Network Administrators and IT Professionals but presented in a format targeted for non-professionals. All the essential networking tools are available in one convenient mobile application."
I have the iPhone version when it was free last time.
I use the LAN scan feature a lot to found out what devices are connected to the same (subnet) network. You can even do a port scan and see what port they are open.
Very practical for a non-JB iDevice. Must download.