The IRS provides PDFs for all tax forms online. Anyone who is willing to do all of the calculations by hand can use them to print out and mail in their tax return.
If you want a computer to do the calculations for you, you have to buy expensive tax software, and you can't easily transfer your data to other programs for the next year.
The IRS should develop a simple, standard language for computerized tax forms and their inputs, and it should publish every tax form in this machine-readable format every year. Software developers will use these formulas to compete with the big tax software companies and develop far better and far cheaper tax software.