This product is listed as “Self-hosted & Open Source”, which is why it does not necessarily have to be European.
Rocket.Chat is a open source team communication service. They offer many guides for self-hosting on different platforms (Docker, Kubernetes, ect.) and clients for Android, iOS, Windows, macOS and Linux.
Stackfield is a team communication service from Germany. It offers end-to-end encryption and apps for many desktop and mobile platforms. It also offers audio and video calls directly in the app.
Infomaniak kChat is a unified communication platform, where you can communicate live with your teams and organize projects in a secure and instant way, from the Swiss cloud provider Infomaniak.
Use the chat in the right bottom corner
