And the people who are employed by tiny companies get paid in only cash, and also do not pay their taxes.

I will admit that "no one" is an exaggeration, but India is one of the worst countries I could think of to try and start a product that helps people figure out their taxes.

Exaggeration and over generalization. You should check with a decent CA on the number of people availing their services to file tax. And just so you know there are 30 million people filing tax returns every year. Quite a low number (in comparison to the population) but definitely not a small market.

So they still don't need this app...

You still have to file tax returns. There are many reasons for that. Just to state one, capital gains doesn't come under the ambit of TDS.

Hmmm, I'm not sure what this means, but all you have to do in Greece if you're salaried is to go online and fill the box with the amount of money you made last year. Hardly something you'd need an app for...

It's not just salary which is taxed at source. We have Fixed Deposits which are incurring interest which needs to be declared. We may have made donations which need to be accounted for. Most of us hire a chartered accountant to do the filing. Therefore a software could be of use.