Alex Stamos should check out https://wire.com (full disclosure: I work there)

• E2EE by default, in groups too

• Has solved the multi device, sync problem

• Has webapp

• Fingerprinting of all devices

• Does not sacrifice features for security - voice, video, media

• Crypto and comms protocols open source https://github.com/wireapp

• Privacy and security whitepaper https://wire.com/privacy