Zotero Standalone Client with the possibility of choosing the sync server address. Instructions based on https://github.com/SamuelHassine/zotero-prime
Modify the file config.sh to register the URL of your Zotero Data server.
For Linux, do the following:
git clone --recursive https://github.com/christian-nils/zotero-sync-standalone.git
cd zotero-sync-standalone
./build.sh
For MacOS and Windows, you will need to change build.sh. Replace all the occurences -p l with -p m (for MacOS) and -p w (for Windows).
After the build, you will find the binaries in ./zotero-standalone-build/staging/Zotero_OSVersion/zotero. You just need to run it and connect to your Sync server (Edit/Preferences -> Sync).