If I may ask, what do you think about Threema?
I thought about it, and I didn't find one.
Lavabit once tried to offer secure e2e encrypted messaging (email), and got a visit. Founder shut it down rather than rat.
https://en.m.wikipedia.org/wiki/Lavabit
Moxie Marlinspike has a positive reputation, but... nah.
There are only two proven business models for secure messaging - confidential location, or confidential informant.