Nuclino is a collaborative document editing service from Germany.
European document collaboration services
A document collaboration service allows users to work together on documents, spreadsheets, presentations, or the like.
This category contains services from companies based in a member state of the European Union (EU), the European Economic Area (EEA) and the European Free Trade Association (EFTA).
You can read more about the listing criteria here.
European services
Nextcloud Office is the document collaboration service of the Nextcloud suite. Nextcloud is a open source file hosting service for self-hosting. Nextcloud Office is part of the Nextcloud suite and is based on the open source tool Collabora Online.
CryptPad is an open source document collaboration service that can be self-hosted. CryptPad is zero-knowledge, which means that the operator cannot read the content written on the site. Since it can be self-hosted there are many instances. The most known, which is also driven by the main developers however is cryptpad.fr.
Self-hosted & Open Source
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.