Slack - A messaging app for teams who see through the Earth!
HeySpace - HeySpace is the only free task and simple project management software with communication and collaboration feature.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Rivers IM - Simple, fast & secure team collaboration platform
Mattermost - Mattermost is an open source alternative to Slack.
Slack for Mac - A new, improved Slack desktop app for Mac