Wire.
* open source, code on github
* e2e encryption (apparently derivative of Signal's Axolotl double ratchet)
* chat/voice/video, and group chats (all encrypted always)
* based in Switzerland, coding out of Berlin
* clients for iOS, Android, Mac, Windows, Linux, Web
* can sign up with phone number or email (or username? Not sure - I think you can find contacts via username, not sure you can sign up without email)
* reasonably responsive on twitter
* yada yada yada