There are also semiconductor reimplementations of some of these classic minicomputers if you was the real thing in a smaller package.

The Harris/Intersil 6100/6120 processor line was basically a highly integrated PDP-8 on a chip. You could get a really cool 6120 kit for a while[1], tho now you'd roll your own, since the kit is no longer being sold.

The TI9900 of crappy microcomputer fame is a implementation of the TI990 minicomputer. There are a couple of example SBCs projects running around.

Data General had the microNOVA version of the DG NOVA. Separately, Fairchild had the F9440. There were dev boards for both, but no open source projects I know of. Software has been an issue for the NOVA.

The WE32000 (not NS32000) was a VLSI implementation of the AT&T 3B5/3B20 minicomputers. There was a dev board, but you'd mostly find one in a 3b2.

And, of course, there were VLSI version of the DEC VAX-11 (e.g. CVAX, NVAX) and PDP-11 (Harris J-11, DEC T-11, several ASIC versions). Found lots of places.

[1] https://github.com/SpareTimeGizmos/SBC6120

Oh, yeah...and the Signetics 2650 (used in some OG video games) was heavily cribbed from the IBM 1130.