You can now make encrypted video calls in Signal, a popular secure messaging app from Open Whisper Systems. It also has support for encrypted chat and voice calling. With the addition of video calling, Signal is becoming a full-featured messaging option as well as one of the most secure options.

This update also makes some improvements to Signal’s voice calling, which hasn’t been perfected yet.

Real-time encryption is almost more straight forward in some ways. A call is synchronous communication that’s somewhat ephemeral which makes cryptography easier.
– Moxie Marlinspike, founder, Open Whisper Systems

The feature can be enabled in the “advanced” settings area. You must enable the “video calling beta.”