Wow sounds like you have done a lot of interesting stuff in the past. I see on your bio that you taught in Trondheim!? So you know Norway then? How long did you stay here?

Yeah relay computer are kind of cool I think since they give a very physical and visible representation of what a computer does.

I got the Turing Tumbler for my kids, as it allows you to simple binary arithmetic stuff using marble: https://www.turingtumble.com

Have you seen the Monster 6502? Some crazy guys implemented the good old 6502 CPU using only transistors, with lots of LEDs to see what is going on: https://monster6502.com

And while we are at it, a project a bit out there but cool for anyone into old school computing, althoug if you did S/360 stuff, maybe you think this is newfangled stuff ;-)

Anyway, this guy did a Z80 multicore system. 16 Z80 cores. The rational was that CPUs where in fact not that expensive then so a multicore system could have made sense instead of using time slicing: http://www.chrisfenton.com/the-zedripper-part-1/