There's also https://whiteout.io/ (open source)

and https://lavaboom.com/ (also open source I think)

Tutanota, Whiteout and Lavaboom are also all from Germany, which I find pretty interesting.

I'm an expat living in Germany. The attitude here is remarkable. There's wide awareness of privacy issues.

You know the joke about how to apply for a job at the NSA? Most of the parents at my childrens' school would get that.