In my country, with an admittedly quite simple tax code, the authorities used to publish each year official COBOL code that computed income tax.
They switched to Java in 2018-ish - and to Github instead of a random FTP server.
Doing your taxes has also been a no-op for many people the past decade or so. You don't do anything except read the tax report, unless you spot some mistakes or items missing in the report that was autofilled by the government, then you can go into the web form and submit the amendments necessary.
Recently helped my dad clear out his office - and we came across a binder with fan-folded, faded dot matrix printed copy of COBOL code he used in order to calculate taxes in the 80s - translating the code to BASIC. The original COBOL code came from the Norwegian tax office - I'm not sure if they still publish something similar.
If memory serves, they updated the program for each year (I guess only numerical constants and small rule changes), but they probably didn't update the source in the documentation.
Here our income tax declaration is very simple, the tax office already knows how much salary we have earned, and there aren't many deductions, so most people either don't have to file taxes at all, or just click next a few times and get their tax returns after a week or so. For 90% of people it takes less than 5 minutes.
They switched to Java in 2018-ish - and to Github instead of a random FTP server.
Doing your taxes has also been a no-op for many people the past decade or so. You don't do anything except read the tax report, unless you spot some mistakes or items missing in the report that was autofilled by the government, then you can go into the web form and submit the amendments necessary.