> I just found that EXEC_AOUT is indeed already configured in std.netwinder...
> 
> Nevertheless, a.out binaries still do not work.
> 
> To come back to my example, ncftp2, I now have the relevant library in the
> path /emul/aout/usr/lib/, but get the same error as above.
>       
> Are there any other 'secrets' involved?
> 

You may also need the following in /emul/aout/etc/ld.so.conf (at least, 
that is what my cats box has):

/usr/pkg/lib
/usr/X11R6/lib
/usr/local/lib

Also, you should still be able to use ldd on the executable.  For example, 
one a.out legacy binary I have reports:

$ ldd gdb
gdb:
        -ltermlib.0 => /emul/aout//usr/lib/libtermlib.so.0.5 (0x2018f000)
        -lm.0 => /emul/aout//usr/lib/libm.so.0.1 (0x20192000)
        -lc.12 => /emul/aout//usr/lib/libc.so.12.81 (0x201b7000)