The -o option sets the prefix to use for the created files. If -o is not specified on the command line, the input file name is used as the output prefix.
hex -W2 app.hzx -Fhex -o app
This splits the application file app.hzx into high and low bytes for a processor with a 16-bit bus. The bytes at even addresses are placed in the file app.0.hex and the bytes at odd addresses in the file app.1.hex.