The website addresses that in the first paragraph. You can, as they did, do it manually yourself. However, you're very likely to make unnoticeable mistakes due

The website addresses that in the first paragraph. You can, as they did, do it manually yourself. However, you're very likely to make unnoticeable mistakes due to it being a government tax form. Using a weekend to do something a computer can do for you in seconds is both a waste of time and likely to make you spend another weekend amending it after they send it back. The vast majority of people just want it to work like it works everywhere else. Computers handle it, and you overwrite anything that the computers can't know so that it's correct. That's what tax software is for, and that's what these projects try to accomplish in a FOSS way.