Go implementation and library of Linux's ip monitor neigh which lists ARP/MAC address changes on network interfaces.
For example:
- Automatically add new firewall rules
- Automatic inventory discovery
- Find intruders
- Configure per-mac address VLANs to your switch(es)
- Gather statistics when device(s) are (dis)connected to/from a network
- Send MAC address to a database
- Send alert(s) when MAC address X is not seen for a while
- etc...