Okay guyz, it has been asked here and there a couple of times, "is there any SDK available for x?", "is there any documentation?" etc. Yes, there probably is, but we may never come across it.
This is of particular interest to me so I investigated a little.
Turns out that there are a lot of ways to program some stuff for retro computers aside from official SDKs and docs, like cross-compilers and alternative platforms (such as CP/M).
For example, "z88dk is a z80 C cross compiler supplied with an assembler/linker and a set of libraries implementing the C standard library for a number of different z80 based machines. The name z88dk originates from the time when the project was founded and targetted only the Cambridge z88 portable." (taken from
http://www.z88dk.org/wiki/doku.php)
Between the list of supported target systems there are relevant names such as MSX, CP/M based systems, Sharp MZ series and Sharp Wizard (OZ/ZQ,
http://en.wikipedia.org/wiki/Sharp_Wizard). Although the NEC PC-8801 / 8001 and Sharp X1 are not listed they are also Z80 based machines, so they could be added in the future in the form of extra libraries (I guess..).
However, C and Basic are not the only languages that can be used.
The elder might prefer some other language such as Fortran, Cobol, Pascal, or straight assembler.
Here's a book in PDF format, "Programming the Z80" (2nd Ed.), by Rodnay Zaks.
I was working into getting up some sort of SDK (rather, compilation of every useful thing out there) for the PC-880x/PC-800x, more work needs to be done before it's actually useful, but soon I'll post what I have, anyway.
As a short introduction to the next chapter (?), as you might or might not know the PC-88 supports CP/M 2.2 operating system, which has it's own type of executables. CP/M is (or was) widespread across old computers, and for CP/M we have Fortran, Cobol and Pascal compilers. Nice!
Extra last minute bonus:
Microsoft FORTRAN-80 v3.4 Manual