Ethereal is a network protocol analyzer, or sniffer, that lets you capture and interactively browse the contents of network frames. The goal of the project is to create a commercial-quality analyzer for Unix and to give Ethereal features that are missing from closed-source sniffers.

License: GPL

Ethereal 0.8.15 has one of the biggest GUI changes in recent history; display filters can now be constructed via an easy-to-use point-and-click interface. Protocol dissectors now exist for: NFSv4, Mobile IPv6, X.25 over TCP, LAPBETHER, DEC LANBridge Spanning Tree Protocol, X.25 over LLC, Frame Relay, MTP3 User Adaptation Layer, and ISDN Q.921 User Adaptation Layer. Many other dissectors and core features were improved, and bugs were squashed. The wiretap library can now read Sniffer Frame Relay files. Capturing supports the "any" pseudo-device on Linux if you use libpcap 0.6.1 from www.tcpdump.org.

http://www.ethereal.com/

http://www.icewalk.com/softlib/app/app_00365.html