Cutware

Cutware is a free network management tool for Windows built to keep your network visible and secure. It brings together an ARP spoofing detector that flags suspicious activity in real time, a network sniffer that captures and inspects live traffic for full visibility into what's happening on your network, an ARP defender that actively blocks and mitigates spoofing attempts as they're detected, and a network controller that gives you centralized oversight of devices and traffic. All of this comes at no cost.