In the hopes of finding a FlexATX board that supported a Pentium III (the one from my modded dot.station) for use in my new router, I discovered these on eBay:
It is essentially a modded Tyan S2425 flex ATX board. It has been modded to allow for a PCI riser, and the IR port was replaced with a custom header (essentially, +12, +5, and the SMbus)
I bought two boards, in case I blow up one trying to get it to boot. As you can see, the BIOS flash is missing. The seller apparently dug up one of the flash memories, and agreed to ship it to me, so if the BIOS code is different, I should be able to flash it into a new part. The great part is (if I can get the board running) is that the ATX stack is missing, but the support components are still populated. It would appear that simply soldering a new connector should restore functionality.
The upside is that it will be easy to add in the vertically mounted VGA port, and it has good parts (i815e with 133MHz FSB, 2 DIMM sockets, no need for the slocket adapter when using newer PIII's, etc) It should also fit power-wise, as it doesn't require the extra 12V connector for a P4 board.
The downside is that I will have to track down USB ports for the rear, and drill a hole for the extra network jack. There is also the issue of audio - this board has no built in codec, but since I don't intend to use the modem, I plan to replace it with a modded PCI sound board. (probably an old yamaha card I have laying around)
Also, I came across the Intel embedded ATX spec on the web:
Alternately, I found ton of gateway flex boards, but those don't have built-in ethernet. I suppose if you don't *need* ethernet, that's great, but...