Unfortunately, I think you’re unlikely to find anything besides the ones made by the big companies: Google, Apple, Samsung, and Garmin are the ones I know. They each have agreements with the banks and credit card companies to handle the secure exchange of data required for the touch payment system. In fact, there are still some issues resulting from a lack of cooperation (such as Citi Bank not working with Garmin Pay because they can’t be bothered to set up the relationship). I imagine an open source software would be unable to get the banks to pay attention to them to establish a partnership, or would otherwise be declined because the financial institutions wouldn’t trust them.