Final answer:
Wireshark is probably the best-known and most powerful free network protocol analyzer for UNIX/Linux and Windows.
Step-by-step explanation:
The correct answer to this question is Wireshark. Previously known as Ethereal, Wireshark is a free network protocol analyzer that is widely recognized as one of the most powerful tools of its kind for UNIX/Linux and Windows operating systems. It allows users to capture and analyze network traffic, helping to troubleshoot network issues and examine network packets in detail.