Self-hostable video/audio calling and chat module within Nextcloud's open-source collaboration suite from Germany's Nextcloud GmbH.
Slack
Project ManagementChannel-based team messaging platform that popularised workplace chat, now owned by Salesforce and sold as part of its suite.
European Alternatives to Slack
German all-in-one collaboration suite combining project management, team chat, and video calls, with end-to-end encryption and hosting in Germany.