Requirements: AppImage, 64-bit, most distributions
Download and install
Download the AppImage
The file Tefter-linux-x86_64.AppImage downloads. Move it wherever you like, for example ~/Applications.
Allow it to run
Right-click → Properties → Allow executing, or in a terminal: chmod +x Tefter-linux-x86_64.AppImage
Run Tefter
Double-click the file. Some distributions need the libfuse2 package.
After installing
Choose: an account or no account
On first launch you choose whether to work without an account (free, data stays on the device) or sign in with your email. You can create an account later and move your data in one click.
Enter your business details
Tax number, registration number, the full business name, address and bank account, exactly as on your APR registration. You enter them once; they print on every invoice.
Issue your first invoice
Add the client by tax number, type the service and amount and issue the invoice. It goes into the KPO book by itself.