Powerful, open-source network protocol analyzer
WinDivert: Windows Packet Divert
tcptrace analyzes packet tcp connections and provides analysis
Xplico is a Network Forensic Analysis Tool (NFAT)
Zero copy MMAP linux network drivers
A MAC address based user authentication system for campus-wide network
...has moved to packetpeeper.org
Simple Multi Protocol Packet Sniffer - SMPPS