DeskAlerts - Send alerts to any corporate device: PCs, phones, tablets, etc.
Ripcord - A desktop chat client for Discord and Slack
Spectrum Chat - A newly open sourced self hosted Slack like alternative for building persistent chat communities
Slack - A messaging app for teams who see through the Earth!
Ziggs - Smoothly Share Content Between Devices!
Mattermost - Mattermost is an open source alternative to Slack.