A few recent posts reminded me of a project I stumbled upon a while back that I haven't seen mentioned much outside of it's home bbs in China so though I'd give it a mention here.
The pages are all in Chinese so heavy use of machine translation may be in order.

The KC-LS1u is a hobbyist developed system based on 74 series logic and is spread across a total of fourteen 100mm x 100mm PCB's stacked tower style.
It's a full system from CPU to VGA to SPI, and even has a mouse driven GUI OS.
The 8-Bit CPU is interesting with it's 24 bit address bus (three address registers in parallel).

It's quite a rabbit hole (an understatement I'm sure) but this might be a reasonable page to start with. The links at the top are full of additional info.
https://bbs.kechuang.org/t/72943?

Some additional links show in a search.
https://bbs.kechuang.org/api/operation? ... ng=KC-LS1u

Quite a few videos here, KC-LS1u vids are in the top half of the page.
http://id.tudou.com/i/UMjUwMDUzODk0OA== ... 244740.0.0

Amazing - a stack of circuit boards, implementing a two-register machine, implementing a full HTTP server??

Hi BigEd, I knew this one was right up your alley.
A later revision adds two more registers, C and D, though they look to be storage only, and not connected to the ALU.

From this thread.
https://bbs.kechuang.org/t/73267

Here's the point where they had the first file transfer with the HTTP server.

https://bbs.kechuang.org/t/69505?&page=3#765750

Fantastic - it seems a very small machine to support a C compiler, but I think they did it - is that right? Is it written from scratch?

There is a compiler, I haven't looked into it enough to see how close to C it is.
I'm not sure if it was written from scratch, I think the whole project is mainly the work of a single person so it's pretty amazing either way.
"KC-LS1uC Compiler V1.0" is listed in a download package here.

KC-LS1uC Compiler V1.0.
HTTP Server Source.
Memory and IO Definitions .
CPU
Instruction Description . KC-LS1u Hardware Protel 99 SE Complete Project File.
KC_LS1u Circuit Diagram PDF Documents are packaged, and the text is followed by Document.

https://bbs.kechuang.org/t/71330

It's very impressive. I did notice a reference to nand2tetris - that's a free course for bottom-up computer building, and I think anyone with some dedicated time and effort could get something from that.

I spotted the nand2tetris link too.
It's impressive just from a hardware point of view, but on top of all that, he's written a mouse driven OS for it.
https://bbs.kechuang.org/t/73726