Around about 2005/6, a bunch of developers forked z88dk to create s1sdk, a development tool chain for the s1mp3 series of devices. These devices were mp3 players powered by the Actions ATJ2085 chip which includes a Z80 clone running at around 25Mhz.
There were two ways of running programs:
1. Replacing a builtin application in the firmware and refreshing it
2. Using the loadram tool to upload a binary to the system RAM
As far as I can tell, there was no 3rd party software released and the project stalled when they tried to create a completely new firmware. Pretty much all websites have now died and these days, the only trace of it can be found in archive.org
Looking for a bit of light entertainment, I found s1sdk, a partial emulator and the loadram tool and resurrected them, the emulator is here:
https://github.com/suborb/s1mulator
loadram is here:
https://github.com/suborb/s1mp3-loadram
s1sdk has been folded into z88dk, and yes, zsdcc can be used to create binaries.
The state of the world for this target is pretty poor, the s1sdk routines to print text and display pictures, there's also gencon available so there's a good console driver available. Other functionality is available via the s1sdk APIs, but the emulator doesn't support any form of input.
I've not access to any hardware, so I've no idea whether the imported functionality actually works. However if someone has some working hardware then the revived projects might be a good leg-up to carry on hacking.