The project commenced in 2024, when [Anders] started a thread on it over at the Exxos Forum which thus became pretty much the project log for the endeavor.
Both RAM and ROM ICs are on SIMM sticks, which seems like a pretty nifty idea compared to the typical socketed or soldered-in approach here, allowing for up to 48 MB of RAM and 16 MB of ROM.
On the custom ATX-compatible mainboard you get a total of 4 ISA slots, as well as everything from YM2149 audio, IDE HDD and legacy Atari peripheral support. All of which fits in a standard ATX case with an ATX power supply. If this tickles your fancy, you can find the design files for the current A1 board revision, though you will have to source your own ICs.
With all of it assembled you can run Atari’s TOS with its GEM UI, or the modern equivalent in the form of FreeMiNT.