None that I'm aware of, and IMO none is likely to be launched any time soon. Email is open and license-free, only because it was invented back in the days when

None that I'm aware of, and IMO none is likely to be launched any time soon. Email is open and license-free, only because it was invented back in the days when not even Richard Stallman saw any need for free software. If email were reinvented today, you'd end up with something very different. It would be copyrighted, patented, and supported by corporations who have strong financial incentives to keep it locked into their proprietary platforms. The only company that I can think of who might have a chance of success at producing an open and license-free reinvention of email is Mozilla, but they don't seem to be particularly interested in email nowadays. Thunderbird has been stuck at version 17 for ages.