The winner of Name that Ware March 2007 is bdb! Impressive work, and congratulations. The board is in fact SN001 of a ChaosNet adapter–one of the direct ancestors of the ubiquitous Ethernet. It’s from a Perkin-Elmers 3230 computer. Needless to say, this is a personal treasure of mine, a small piece of history that I can call my own.
While some ChaosNet adapters were deployed in Symbolics LISP machines, I was specifically looking for someone to identify it as a ChaosNet adapter (so John Peterson was very close, but bdb nailed it right on). Congratulations again!