I've been reading that ion-exchange softeners are being outlawed in some jurisdictions, e.g., Santa Clarita, CA, due to the salt impact on water re-use. I'm aware of ion-exchange softeners being used with potasium , but I believe it has the same problems as sodium chloride. So called "salt-free softeners" are being sold, including the Life Source product that uses some magnetic principle, which I've read is not scientifically sound.
So the question is, is there any such thing as a salt-free water softener, other than RO?
Perception is 3/4 of reality
If you define soft water as the absence of calcium and magnesium ions then the only water softeners are systems which remove those ions--that includes conventional water softeners which exchange sodium or potassium ions for calcium and magnesium and RO and distillation. The "salt free" systems I am aware of generally don't claim to soften the water if you read the claims carefully--rather they claim to diminish some of the effects of hardness in the water such as scaling or creating hard to remove water spots.