You're right, brobotics. I don't think any Lemurian computers gave details on the ACoNR. But they referred to Lemurians playing around with technology that they didn't fully comprehend. This bolstered the idea, for me, that ACoNR contained such technology, and that corporations may have endangered people by experimenting with it.
It wouldn't surprise me if ACoNR was used to create Underrail. Wasn't one used to create Lemuria? I can't remember now. But Underrail is perfect for what an ACoNR would be used for: rapidly constructing a habitat / ecosystem beyond what contemporary science can provide.
I wonder how much of Underrail, in that case, would be ACoNR-created, and how much would be created by the corporations? Would Biocorp find a deep underground cave system, and deploy ACoNR, or hollow it out first with nukes? Or would the digging and shaping be left to the device?
I guess if ACoNR created cave systems, lakes, oxygen replenishment systems, maybe the basic wildlife and fungus / mushrooms, humans could move in and build cities, rail, etc... ACoNR being used to create both Lemuria and Underrail separately would show why the base systems (caves, lakes / sea) were similar, but the building styles were different. [I seem to recall reading that NFT created Lemuria, probably with the aid of exotic devices, and were surprised by Biocorp finding them. Why did they create it so close?]
This also shows why it would be a terrible idea to open an ACoNR in Underrail. Underrail is one of humanity's last surviving habitats. And the ACoNR could be configured for something completely different. There are a number of analogues to it in science fiction.