SureSpot!

Riot (formerly Vector) is an opensource interoperable app running on Web, iOS and Android. It is built around chat rooms, both public and private and provides messaging, filesharing, voice and video conferencing (beta on Android and web), integrations to tools like GitHub, Jira, Jenkins and much more soon. Vector is built on the Matrix.org open standard which provides bridges to other systems such as Slack, IRC and a lot more soon. One can use the hosted service or run their own. »

ChatSecure is a free and open source messaging app that features OTR encryption over XMPP. You can connect to your existing accounts on Facebook or Google, create new accounts on public XMPP servers(including via Tor), or even connect to your own server for extra security.

Threema is a new mobile messaging app that puts security first. With true end-to-end encryption, you can rest assured that only you and the intended recipient can read your messages.

Zulip is a group chat app.

Wickr is a free end-to-end encrypted text, video, picture and voice messenger with full sender control.

Technitium Bit Chat is a secure, peer-to-peer (p2p), open source instant messenger designed to provide end-to-end encryption. Primary aim of developing this instant messenger is to provide privacy which is achieved using strong cryptography. It can be used over Internet and private LAN networks for instant messaging and file transfer.

Cyanide is Tox client for Sailfish OS .

Dasher lets you do more than just text message. It's messaging with benefits:

Sesame is a messaging app that gives you a self-aware digital assistant to protect messages on your behalf: your own Personal Cognitive Messenger™.

WowApp helps you do good through the Power of Sharing. We share all revenues with you. WowApp Messenger is free and you can receive earnings without ever spending money.