A few projects that I'm aware of (disclaimer: I'm involved with LEAP):

- https://pixelated-project.org/

- https://www.mailpile.is/

- https://modernpgp.org/memoryhole/

- https://inbome.readthedocs.io/en/latest/

- https://leap.se/

Edit: btw, if you're in Berlin from 14-18 Dec, drop by the AME2016 unconf+hackaton https://github.com/mailencrypt/ame2016