The z88 operating system, OZ, provides a lot of functionality for programmers which permit multiple applications to co-exist and conserve resources (i.e. memory) as necessary. z88dk aims to hide away a lot of the details and provide a relatively simple solution to developing of applications.
For details of the functionality OZ exposes, it's advisable to read the Z88 Developer Notes. The notes describe a lot of detail that is skipped over here.
By default, z88dk generates binaries that can be LOADed into the BBC Basic application and run. Using this target is the easiest way to get an application up and running on the z88.
Z88dk can be used to create a z88 Applications that can be run from the Main Menu. Both good, bad and ugly applications can be constructed.
zcc +z88 -create-app -make-app
As for applications, i.e.:
zcc +z88 -create-app -oapp.bas -make-app app.c
The z88 shell is a unix-like shell providing command line file manipulation on the z88. Naturally, z88dk supports generating applications that can be run from the command line.
zcc +z88 -subtype=z88shell -create-app
ZSock devices can be compiled with z88dk, these are raw binary blobs that sit at address 8192 and cannot use a stdio resources.
zcc +z88 -subtype=zsockdev
Z80asm can include a relocator to the head of a generated binary. This will cause the code to be relocated to the address that it is loaded at and then run.
zcc +z88 -subtype=reloc
zcc +z88 -clib=net