Twist - Check fewer notifications, do more meaningful work. Twist is the team communication app for calmer, more organized, and more productive teamwork.
Slack - A messaging app for teams who see through the Earth!
P2 - Share, discuss, and collab with your team. By Wordpress.
9mCollab - Collaborate (efficiently) Conclude (fast) Contribute (in the knowledge base)
Mattermost - Mattermost is an open source alternative to Slack.
Redesk Beta - Async-first messaging app with goals, deadlines and upvotes.