Borax is a naturally occurring mineral, but is toxic. You should always wear gloves when working with it as it absorbed through the skin and takes a long time to work its way out of your system. Keep it away from children, and no matter what you read on the Internet, never bath your pet in it. I have listed it here during eco-cleaning week because it is a natural salt, but it still is dangerous and must be handled carefully.
Borax is good at cleaning tubs, carpet stains, sinks, and mildew. It works great as a laundry booster and is an ingredient of many brands. For laundry it works especially well on curry, strawberry, raspberry, blueberry, vomit, and red wine stains. It also works as a deodorizer for carpets and cloths. I use it most often to remove the rings in my toilets.