The SNES had a wacky dedicated sound controller CPU that's a full CPU but as far as I can tell nobody else ever used it for anything, not even Sony, who manufactured it in the first place
If that o_o is at me: I've been doing SNES homebrew nonsense recently! But its main CPU, while _also_ wacky and only used in one other system of any significance (the Apple IIgs), that one other system is one I _do_ have some experience with