See I knew there most be a reason people have it installed.
I didn't know they did that in the US. I knew my government was probably pretty unique anyway.
My government has a program people can download from their website so people can do their taxes.
I haven't done my own taxes the last couple of years, but this program used to be based on some open source components (there was at least a license file which made that very clear) and it was thus available for Windows, Mac and Linux (I wouldn't be surprised if you could run the Linux program on BSD with Linux emulation as well).
You could print the result or submit it over the Internet.
I just downloaded the one for 2011 and it seems to be mostly a bunch of HTML-files with a program around it (it also has a license file which says it used LGPL software) and it is still available for Windows, Mac and Linux.