Spiceworks, Solar Winds, and Cacti are all well-known effective network monitoring tools. A lesser known company called Lizard Systems has quality software for network monitoring. Techworld.com and PCworld have favorable reviews of Lizard Systems' Network Scanner. The Find Mac Address product has an easy installation and can find MAC addresses without network administrator rights to a given router. For an alternative to Nagios or Sysinternals, you may want to try Remote Process Explorer. Lizard Systems' server monitoring solutions primarily focus on Microsoft Windows servers and desktops. But for finding an IoT device MAC address on a router you do not have network administrator access to, the Find Mac Address product is excellent.