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.