Homemade liquid sweetener from Stevia
I buy bulk pure Stevioside powder online. It's much cheaper to buy the pure powder that way and make your own stock solution.
I make my stock strong enough so that 1 drop equals 1 teaspoon (4g) sugar in sweetness, 3 drops per tablespoon (12g).

For 100 ml:

23.5 gram Stevia powder

20 ml 95% ethanol

Bring to 100 ml with water.

The alcohol is added both because Stevia isn't that soluble in plain water, but is in 20% ethanol, and as preservative. I've kept a single jar for over three years now, opening periodically; no mold, no growth problems.

I find the powder just too fiddly to work with in the kitchen; tiny scoops, or always weighing out 100 mg. Plus the pure powder likes to puff up into the air. A good strong stock solution is far easier to handle cooking-wise.

Note: bottle lasted through June 2016 at room temp, with no spoilage or degradation. So 2-3 year shelf life, at least.