Atari ST was used to develop games for CPC.
Raphael Cecco, creator of Exolon or Cybernoid series was known for programming on Atari ST then channel codes into the CPC . http://cpcrulez.fr/games-auteur-raffaele_cecco_ACPC.htm (he said this in interviewsFrench).
Also Loriciel developped Hardware tools for such 16bit-computer helped developments, as seen on this picture :