> I agree that this is a great idea, provided someone else does it.  :-)

I can draft one if it doesn't matter that it may take a month. I've used
the WinAPI error functions which may help a little.

The pet feature I'd like to have is retrieving errno values from
standard RnRS I/O procedures; I'll need some input from more experienced
Schemers for how to best accomplish that. Probably the SRFI should
specify an (os-error? <some-exception>) procedure to which exceptions
from RnRS I/O procedures can answer #t.

I think libexplain was the name of that friendly-unix-errors library you
linked some time ago. It'd be nice to draft a SRFI on top of which an
equivalent pure-Scheme library is easy to implement.