Over in my corner, we have a State provided income tax simulator and filer. Not too pretty, but correct and useful; it's done in Java and runs under Windows, MacOS and Linux.

It's been so successful that most tax returns are nowadays filed with it, and quite a few public offices where people used to queue up to file their (paper) returns have been closed. There was never much of a setup/tradition of filing by mail like in the U.S.

Over the last couple of years, they've improved data cross-referencing to the point where I can get most of my form pre-filled from the government.