relay-based logic boards, transistor-based logic, 74LS stuff, finally FPGA
or at least hinting towards development of some kind of computational unit with an alternative architecture: for example hardware in some way mirroring the cons cells of lisp. binary hardware logic mirroring some other structure itself. in silicon.
from here:
http://constantly.at/blog/2006/07/05/ecoop-06-lisp-workshop-in-brief/
to here:
https://www.gelato.unsw.edu.au/archives/comp-arch/2006-May/000903.html
and then to these:
http://www.frank-buss.de/lispcpu/
http://vaxbusters.org/workshop/home.xml (and links also to transputer implementations within an FPGA)