armb's journal

Turing machine: http://mapageweb.umontreal.ca/cousined/lego/5-Machines/Turing/Turing.html

[Edit: Also at http://gadgets.boingboing.net/2008/06/12/lego-turing-machine.html, and actually a variant machine provably equivalent to a Turing machine.]

Babbage engine (bits of): http://www.cclrc.ac.uk/Activity/MAD;SECTION=8574;

[Edit: latter link now dead, http://www.stfc.ac.uk/PandS/SchEdu/MAD/involved.aspx has a mention.]