Official tax software for German tax-payers with an online module which did the data exchange with a tax office. It is for paperless tax declarations according to the tax system in Germany and only available in German language.
As a German tax payer you will have to use eigther an online version in the web or this software. This is the reason why you will find here in AppDB only reports about the latest version. There is no way to download old versions and also this isn't supported or desired by any tax office.
Elsterformular is written in Qt, but a Windows only application.