It isn't the software that is complicated, it's the intricate knowledge of the tax laws at the Federal and state level that goes behind building it. If you can find a team of lawyers and tax accountants willing to work on it for free (and update it every year) then building something like TurboTax wouldn't be too difficult.
Open source software can be paid for. With a bit of funding, I bet an OSS-clone of TT could be produced and the organization can host and offer e-filing for a nominal fee.
I think the IRS will actually pay a service fee to small companies that file the free federal returns for individuals.
