UsTaxes is an open source tax filing application that can be used to file the Federal 1040 form. It is different from paid tax preparation software in that it protects user privacy and is provided for free. It is available in both web and desktop formats.
The coolest thing about this (in addition to it being free-as-in-beer) is that it stores all data in the browser only, so your personal info never leaves your computer.
WIP Alert: You shouldn’t use it file your taxes for the 2020 / 2021 tax season, but it’s a great time to get involved and help this software become production-ready for the next go-around.