I concur. A development methodology ("open source") will not address any of the deficiencies (when viewed from the voter's perspective, the perspective that should matter most) of voting. No matter how much one trusts a voting program, there's no way to be sure that the computer used for voting is running only software one trusts. No electronic system can compete with the simplicity and recount-friendly approach of what is called for here: voter-verified paper ballots.
So address to the question in the
There are computers one can purchase that do as the parent post specified—the voter feeds in a blank ballot (one which they could have filled out manually if desired) and the computer (which has a scanner and printer attached) will scan the ballot, help the voter by showing the choices on a screen, reading the ballot aloud, or reading the ballot text to headphones, and then collect votes from the voter. Then the computer's printer will print the voter's votes on the paper ballot, and eject the printed paper ballot to let the user inspect that printed ballot. At this point the voter can choose to carry the voter-verified paper ballot to be counted or spoil that ballot and start again. The voter can also feed in a marked up ballot (marked by hand or by computer) and let the computer summarize the votes which that ballot specifies. These features let the blind and/or illiterate vote without losing their privacy by forcing them to find & bring in someone else to mark up their ballot for them. This is as close to computers used in voting as one should want to get.