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The IBM CS 9000. https://en.wikipedia.org/wiki/IBM_System_9000 When I interned @IBM in the mid-80s we had a (computer) lab full of these things. Each had a 68K CPU with (I think) 128K of RAM, a little mono green monitor, and external 8" floppies for storage. All of them running the multi-tasking CSOS operating system.

I never hear them mentioned these days which strikes me as odd though it may be just that I'm not really plugged into the vintage community. It could also be that there are simply none to be had anywhere now. I never hacked on them myself - we already had quite a few 1st-gen PCs in the lab and I worked on those. I seem to recall that our CS9000 app devs were coding in some version of Pascal (possibly cross-compiled from a mainframe) and that there was some form of proprietary connectivity with the site's local System/370.

At some point the lab also obtained a "portable" PC (https://en.wikipedia.org/wiki/IBM_Portable_Personal_Computer) which was a god-awful, big, heavy beast. However I can't say that I find those "interesting" and IIRC most of the devs even then were mainly interested in avoiding having to use it.

I used to think it was strange that, considering it was already selling CS9000s, IBM didn't base its entry into the general-purpose PC market on a stripped-down version of the hardware and on CSOS.