AstraChat is an enterprise chat and messaging product that provides privacy and security out of the box.
Mattermost - Mattermost is an open source alternative to Slack.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Digsby - Tagged makes it easy to meet and socialize with new people through games, shared interests, friend suggestions, browsing profiles, and much more.
Slack - A messaging app for teams who see through the Earth!
Facebook Messenger - Facebook Messenger is a faster way to message.