Does it provide a graphics server in the absence of all the X11 foundation libs? TBH, I've only played with microwindows in DOS, OSX with XQuartz, and Linux with X11.

Yes. With the caveat that my knowledge of Nano-X is about 20 years out of date: It very specifically is not X, though the API is close to the Xlib API, and there's a shim that provides some X11 compatibility, and of course on the backend there's an X11 driver.

But it only requires a driver that can handle a minimum of reading/setting individual pixels and draw horizontal and vertical lines and manage the palette (of course if whatever you're drawing on supports more than that, you'll get far better performance if you implement e.g. blits).

We were using it without any shims, and had a very tiny GUI lib running directly against the Nano-X API, and contracted Opera to port their browser to it as well to use on our tablet.

It was a fun project, but way too early - the hardware we built was beautiful but so extremely constrained, leading to put a huge effort into shrinking everything. Never made it to mass production.