Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.
Pandora - Pandora Radio is a free (ad-supported) internet radio founded in 2000.
ChatSecure - ChatSecure is a free and open source messaging app that features OTR encryption over XMPP.
Keybase Chat - End-to-end encrypted chat built into Keybase
Pithos - pithos is a daemon which provides an S3-compatible frontend for storing files in a Cassandra cluster.
Otr.to - A secure peer-to-peer chat in your web browser.