Ethereal is a GTK+-based 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. Screenshot available here.
727a74757999d359b589a3f4670c257b0eccbd1af4fadbc5fc12eb568d101081