In 1936 Alan Turing invented a machine that could manipulate symbols on a strip of paper/tape according to a set of rules. This seemingly simple accomplishment (by today’s standard) set the groundwork for all future computer processing and algorithms. Turing never built the machine as the importance of this achievement was in conceiving the theoretical how it would work not in the practical material application.

Since then his machine has been realized… now in Lego.

The (LEGO) Turing Machine Comes True by CNRS via MakeZine

The above example is using pneumatics, while the one below a Lego Mindtrorms driver…

http://www.legoturingmachine.org

Build your own here.