Rather than me explain it all why not go to the source?
The hardware ANS was named after Alexander Scriabin, who mixed the occult with piano to good effect. It is a formidable piece of engineering with a whole heap of mythology behind it. Fortunately this virtual version is much simpler and quickly reveals it’s all based upon a chart of harmonics over time. Basically the ANS is an additive synthesiser where you paint the harmonics in by hand. Because your hand is wobbly and uncertain the sounds it makes are wobbly and uncertain. You will be ready for Halloween.
Most additive synthesisers work hard to hide the complexity of their function. The virtual ANS has none of that. You will paint by hand! Draw mystical symbols! It is free to use so take the challenge. At least on the iPad the doodling seems quite natural and suited to the touch screen. But your fingers will never quite be slim enough.
Some readers will notice a comparison with MetaSynth, an extensive and powerful drawing synthesiser sold by U&I Software. This provides a wider range of wobbly incompetence than the ANS. I gave up updating MetaSynth around version 5 as the authors seem overwhelmed by updates to the Apple operating system and can only be resuscitated by injections of money. I understand Apple is a PITA but everyone else seems to be able to get on with it, more importantly I don’t seem to have done much with the older versions and should admit defeat. The latest version is here.