HedgeDoc is an open-source, web-based, self-hosted editor for collaborative Markdown notes. Several people work on the same note at once, with a presentation mode (built on reveal.js), diagrams, a simple permission setting per note and revision history. HedgeDoc has modest server requirements and can even run on a Raspberry Pi. You install it on your own server with a ready-to-use bundle or a Docker image; a public demo instance is also available.
HedgeDoc is free software under the AGPL-3.0 licence and is developed by volunteers within its own GitHub organisation. The project grew out of the HackMD community edition, was later called CodiMD and was renamed HedgeDoc in 2020. No commercial provider stands behind it, so you host it yourself and the data lives wherever you run the software. Version 1.x receives maintenance only; HedgeDoc 2 is a rewrite that is still in alpha. For a European organisation, self-hosting gives full control over storage location and access, but also the duty to keep up with updates.