WhatsApp Messenger!

With Viber, everyone in the world can connect. Freely. More than 460 million Viber users text, make HD-quality phone and video calls, and send photo and video messages worldwide over WiFi or 3G - for free. Viber Out can be used to make calls to non-Viber landlines and mobile numbers at low rates. Viber is available for many smartphones and platforms.

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. »

Facebook Messenger is a faster way to message. Reach friends right on their phones, get and send messages fast, message everyone at once and more.

Trillian is an instant messaging app that works on phones, tablets, and desktops while keeping your chats neatly synchronized between all of them! We think conversation should be easily shared between all of your devices, not trapped as text messages on your phone. Here's how we do it:• INSTANT MESSAGING: Your unique Trillian username can be used to send unlimited messages free of charge. Trillian uses your existing data plan and/or WiFi.• ANYWHERE: Trillian's continuous client feature delivers your chats instantly between all of your connected devices. In addition, Trillian automatically silences push notifications on mobile devices if you're active on a desktop - no more dealing with a phone buzzing on your desk all day!• SIMPLE: Trillian places a strong emphasis on fast and reliable message delivery and a beautiful, easy-to-use interface.• SECURE: All communication with Trillian servers uses TLS to ensure third-parties can't read your chats.• INTEROPERABLE: Of course, Trillian wouldn't be Trillian without support for Facebook Chat, MSN, Google Talk, AIM, ICQ, Yahoo!, and Jabber. »

Franz is a free messaging app / former Emperor of Austria and combines chat & messaging services into one application. Franz currently supports Slack, WhatsApp, WeChat, HipChat, Facebook Messenger, Telegram, Google Hangouts, GroupMe, Skype and many more. You can download Franz for Mac, Windows & Linux.

Matrix.org is a growing ecosystem for open, decentralised chat, VoIP and IoT communication.

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.