Homemade CPUs...

Here's a nice post (with photos) of some made-from-scratch CPUs (including one made entirely from relays!).  I've often thought of doing something like this myself, just for fun.  I can add one to the list: back in the mid '70s, I worked with Don Tarbell, one of the microcomputer pioneers.  He's most well-known for the Tarbell cassette interface and the Tarbell floppy controller.  I wrote a Basic interpreter for him, which he distributed with the floppy controller and as a standalone product.  Don had an all-TTL homebrew CPU in his offices, something he built in the early '70s just for fun.  At the time, I couldn't imagine anything more intriguing than a project like that...I spent hours with him just poring over the details.  He greatly enjoyed having an interested person to talk about it with...