Water conditioners vary from being expensive snake oil devices that do little or nothing, through devices that seem to be based on pseudoscience to devices that do seem to be able to temporarily change the way that calcium carbonate forms when water is heated or evaporates. These conditioning devices don't soften the water at all, it's just as hard, so needs the same amount of soap/detergent, they just tend to reduce the amount of scale that builds up.
The third type of device is a phosphate dosing system. These work well at making the water appear softer, so making soap/detergent work a bit better, but again they don't actually remove calcium and magnesium ions from the water, so they don't soften it as such.
Finally, there are reverse osmosis systems that can remove pretty much everything from the water, but they are only really suitable for low-flow applications, and the water they produce may not be everyone's cup of tea (literally, it doesn't seem to make a decent cup of tea).
