I've worked for some characters in my time, and some of my elderly bosses were hardcore on this subject. As it happens, in various industries - rail/transportation, for example - there are often available large surpluses of electro-mechanical relays, in copious quantities sitting in large bins, which .. by way of practical application of apprentices .. become a new 'test subsystem rack' waaaaaay in the back of RailtrainCo.'s, computing facility. What I'm trying to say is, "don't power off the back racks, ever, because they are the bosses little relay-CPU project, and its computing .. something .. (actually its running the model railway switching system, upstairs in the lobby)" ..

That sounds like something from a Charlie Stross Laundry novel.

Edit: I have encountered systems that were designed in the 1960s where they wanted to rely on tried and tested technology - so pretty much clockwork! This was for sequencing operations during the emergency shutdown of a nuclear reactor, so being conservative in technology platform was perhaps understandable!

Remote reprogramming requiring a metal lathe, milling machine, and a cooperative operator onsite is not necessarily a bug with nukes. Expensive, but accidents are more expensive.

In my case, it was just so that the Boss could prove the point: even his relay-CPU could handle the train signalling/switching systems, sometimes, better than the 'modern' versions we were all sweating on developing. Technological prowess runs deep in the train-nerds world.

Notice most of the wire-wrapped machines are 8-bit data 16-bit address, or similar. 32-bit gets pretty painful to do on a proto board.

I know a guy who is building an All Relay Computer, no transistors.

I don't think he has a webpage though.

"Or y'know build a really, really slow one out of parts that you could actually use in your home."

He already said that. He's pointing out this isn't a physical build since that requires parts as mentioned above or a fab run.