I think it's pretty common.  I've seen quite a few of these around.
I built 2-3 Z-80 cards for Apple IIs using $5-$10 clone circuit boards.
It cost only a few dollars to stuff the cards with parts.  You might
still be able to find the bare cards around.
Dave
Lawrence LeMay wrote:
 Well, I just bought something at a used bookstore called "SOFTCARD; VOLUME II"
 Its a microsoft product, and apparently its illegal to even give it away,
 let alone to resell it ;) I'm going to ignore that obviously illegal
 wording ;)
 Apparenly this is the software and manual for the Microsoft Z80 card
 for the Apple II series. I have one floppy disk, never used, in
 16-sector format for DOS 3.3 or language card. Apparently there should
 be another manual with chapters 1-3 (unfotunately these are the
 more interesting chapters), whereas this is chapter 4 on the latest and
 greatest microsoft basic ever created, which is apparently on the
 floppy disks ;) plus a little information in the final chapter 5.
 I dont suppose i can use any of this without the Z80 card? The cp/m wont
 work without it i'm guessing. Am I correct in guessing all this is
 good for is Ebay or trades?
 -Lawrence LeMay
 PS: I also picked up a nice copy of "the programmers CP/M handbook" which
     provides extensive coverage of CP/M 2.2, mainly assebly listings. It
     looks like more than 50% of it is assembly listings. Interesting...
 PPS: I really should go back and buy that UCSD P-system book, I suppose.