I recently had a conversation with a friend and casually mentioned the IBM PC/XT-386. He'd never heard of it. So I got to thinking...what other weird PCs had I run into over time. Here's my list of machines I personally worked with:
IBM PC/XT-386 (late 1986) - A 16MHz 386 chip on an 8-bit XT motherboard. Acted like a supercharged XT and had all normal RAM and AT-bus speed issues to boot. AFAIK, only purchased by DP managers inordinately influenced by IBM on-site staff.
DEC Rainbow (1982) - A Z80 and 8086 (or 8088?) in one box. It could run CP/M, DOS, and could also boot into some sort of dumb terminal mode. Had a PITA floppy drive, as I recall, that threw out a lot of read errors. Popular for word-processing, though.
Apple III (1980) - Pretty high-powered 8-bit business machine for it's time but had severe reliability problems. Used an OS called "S.O.S" which, I forget what it stands for, but we called it the "S**t on S**t" OS. I once had a buttload of these surplused in my garage.
IBM Personal Portable Computer (1983?) - We called it the "Luggable". The built-in screen was amber, not green, and surprising legible. Had half- or third-height floppy drives that you couldn't use to format normal floppies. They could read and write normally, but disks formatted in the Portable were unreadable by desktop IBM PCs. I was working on a project all summer of '84 from home with this.
AT&T PC6300 (1985) - A client of mine standardized on these machines in early '85. The HD controllers and HDs broke down constantly on these ugly things. It was AT&T in name only; once you popped one open it was all Olivetti.
NEC MultiSpeed (1985?) - My first "laptop". Had twin 720K 3.5" floppies and a B&W monochrome screen. 512K of RAM I think. I'd sit by my apartment pool with a bootable disk with MFOXPLUS in one drive and my project in the other and code away....that is for about 35 minutes, when the battery failed. I was single at the time and this was the only way I could look "cool" at the pool.
There were others who's names escape me now. Please add to the list!