Some fiscal invoicing program

I'm planning to switch my father's main work PC system from Windows to Zorin, Zorin already has everything I need, I just need a tax billing program, I've searched everywhere and can't find any alternatives, do you know of any ? ? ? ? ? ? ?

I have no recommendations other than a web search... as I have used none of these.

Try Contasimple Desktop its in the Zorin Software Center, its a CRM billing, invoice and tax software, i know it has tax forms in it, I dont know if it has the ability to efile directly from the app though. Its more for tracking sales taxes but also generates reports.