WhoIsConnectedSniffer is a network discovery tool that listens to network packets on your network adapter using a capture driver (WinpCap or MS network monitor) and accumulates a list of computer and devices currently connected to your network. WhoIsConnectedSniffer uses various protocols to detect the computers connected to your network, including ARP, UDP, DHCP, mDNS, and BROWSER.

via WhoIsConnectedSniffer.