I had a CompuPro 8-16 with double 8" floppies, and a Viasyn 286, both running Digital Research Concurrent DOS.
My development system was a Computer Innovations C-compiler, and a large Facit 9600 baud (you're supposed to gasp) terminal capable of displaying Wordstar files without locking up (new gasp required).
Though the 386 ushered in the demise of the S-100 bus, Concurrent DOS lived on for some time, renamed to Real32.
Thank you for letting me relive those memories. Now, I'll wipe a tear from the corner of my eye and continue chasing that PCINT. (Wow. It has an FMUL instruction! That's mainframe capabilities.)