SODA CRYSTALS! 
I bought them to add to my white washing as I have old and grey white towels I wanted to get stains out of.
I looked on the back of the packaging (here's why I'm so excited) and it seems they can be used for anything from cleaning to getting moss off brick walls. I'm going to Google the brand to see what else they recommend but I was wondering what everyone else finds them really good for and what to give a miss.