Vidyo!

WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for iPhone, BlackBerry, Android, Windows Phone and Nokia and yes, those phones can all message each other! Because WhatsApp Messenger uses the same internet data plan that you use for email and web browsing, there is no cost to message and stay in touch with your friends.

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. »

Linphone is an internet phone or Voice Over IP phone (VoIP). With Linphone you can communicate freely with people over the internet, with voice, video, and text instant messaging. Linphone makes use of the SIP protocol, an open standard for internet telephony. You can use Linphone with any SIP VoIP operator.

See up to 8 friends on live video while chatting with them! Create your own room (appear.in/your-room) and send the link on chat, Facebook Messenger, SMS or email to invite people. No registration required, once people click the link, they'll appear with you!

Zulip is a group chat app.

Voxeet has created a new generation sound technology that makes audio conferencing for distributed groups as natural as face-to-face communications. Voxeet offers affordable, crystal clear business quality conferencing services with one touch click-to-mobile.

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

Jump into a video chat with your friends without the need for creating accounts. Chat using just a WebRTC supported browser or phone.

SeaFour is the SeaFour.club community's chat engine, powered by Node.js and Socket.io.It's a socket webchat supporting aesthetic username customization and stylized messages using a markup language similar to 'LISP', and supports a multitude of alternative clients. It uses a free-as-in-freedom license that enables users to modify the software to best fit their needs.

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

BroadSoft MobileLink is a simple non-VoIP client that enables end-users to make and receive calls over their existing cellular service using their business identity. Users can dial and manage calls from their personal smartphones just as they would from their office desk phone, including tracking calls, picking up business voicemail, managing personal settings, and more.