Slack - A messaging app for teams who see through the Earth!
Mattermost - Mattermost is an open source alternative to Slack.
Flock - A faster way for your team to communicate
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
RingCentral Video - Live life unlimited. Free video meetings and team messaging in one app that works the way you do.
Flowdock - Chat & inbox for teams. One place to talk and stay up-to-date.