The tool sends ARP Packets to every IPv4 address in the range and looks for the mandatory ARP Reply.

You are limited to scanning IP addresses in your subnet - why? Because ARP is not routed. IPv4 connected devices cannot hide from ARP - the must respond if they are to be communicating using IPv4 ethernet.
 

It displays ARP replies with the corresponding IPv4 address.

Shows all devices responding with an ARP reply message during the scan. The manufacturer of each remote device's network interface is shown. The hostname for each IP address can be optionally shown.
 

Make notes or comments to go with each MAC address.

You can add a note that is tied to each MAC address so if the IPv4 address changes in a DHCP environment, the note will stay with the MAC address.