Epsom Salts (Magnesium Sulphate).
 
Use in baths to soothe sore muscles.
 
Use as a bathroom scrubbing powder by mixing with soap and baking soda or bicarbonate.
 
Clean toilets by mixing with some washing up liquid and leaving in the bowl for 20 minutes before scrubbing with the toilet brush.
 
Use in the garden to fertilise plants and repel bugs.