Etherpeek is a great packet capture utility for classic Macs. It allows you to monitor the traffic flowing over a network and capture it for later analysis.
Predecessor to products like Ethereal and Ettercap. Etherpeek was later renamed as a company to Wildpackets and still exists today.
A great MacTech article about the product is readable at http://www.mactech.com/articles/mactech/Vol.16/16.03/EtherPeekMicroscope...
Archive contains a .img of Etherpeek 4.0 with the installer as well as a manual and quick tour PDF, the updater to 4.0.1, and a patcher for 4.0.1 to remove the need for a serial. Requires a Power Macintosh running Mac OS 8.0 or later.Compatibility