Open-source software is simply software for which the original source code is made freely available and may be redistributed and modified. In the case of voting, open-source software systems would be overseen by public-private partnerships between counties and vendors.
Open-source systems are tried and tested. A majority of supercomputers use them. The Defense Department, NASA and the United States Air Force all use open-source systems, because they know this provides far more security. Every step in our voting process should use software that follows these examples.