This product is listed as “Self-hosted & Open Source”, which is why it does not necessarily have to be European.
Collabora Online is an open source document collaboration service. It can be self-hosted and is used by many cloud solutions like Nextcloud Office. They offer a text (Writer), spreadsheet (Calc), presentation (Impress) and vector graphics (Draw) editor.
Infomaniak kDrive is the file hosting and collaborative document editing service of the Swiss cloud provider Infomaniak. The document editing service if based on the open source tool OnlyOffice.
Proton Docs let you collaborate in real time, leave comments, add photos, and store your documents securely. Proton Docs and also the spreadsheet product Proton Sheets, is part of the bigger Proton Drive product.
