Pure vinegar. Use just a sponge or rag, if you don't have a spray bottle. You can recycle a spray bottle, or buy a good one, where the pump will last a while, at NAPA, for just $2-3.
Vinegar and baking soda makes a good scrubbing past for some things, such as kitchen counter stains, and is nice because it's not too damagingly abrasive, as are some scouring powders.
But, for hard water stains, which are mostly calcium, you don't want to neutralize the acetic acid with the baking soda; you want the full strength acetic acid to dissolve the alkaline calcium.
Best thing is to keep a spray bottle handy, and use it as your regular cleaner, to keep the hard water stains from building up. One advantage of vinegar is that it won't hurt your hands, so you don't need gloves. Heck, you can drink the stuff.
Vinegar will kill 99% of the germs on a floor; I imagine it will do a pretty good job of that on a toilet or sink, too. I use a spray stream on my floor, to. I just walk around squirting it on the floor, then use a wet mop.
Best way to clean a microwave is to put a small dish of vinegar in, heat for a few minutes, then wipe down. I've found the cheapest place to buy gallons of white vinegar is Sav-A-Lot. Get several gallons at a time, and use freely.
It acts as a water softener (neutralizes the calcium in the water), so if you add to laundry, you need less soap, it cleans better, and the soap rinses out better, and it stops the dingy soap scum buildup which can be noticeable on whites, so you don't have to bleach as often. Once it evaporates, in the dryer or on the line, it leaves no odor. Don't use brown vinegar; it stains. There are many sites online, with titles like "101 uses for vinegar'. They'll tell you what concentrations to use, and when to mix with other things, such as soap, for different jobs. Useful, versatile, cheap, nontoxic, and effective stuff!