Nextcloud

• https://docs.nextcloud.com/

Nextcloud is a cloud-based "file sync and share software". It offers

• syncing of OS-based directories (Linux, Windows, macOS) with the Nextcloud server ("Desktop Sync client")
• a browser-based desktop (the "Web interface") with various "apps".

apps

• Files: the (synchronized) files on the server
• Photos: organization of images
• Activities: a log of changes that happened in the apps -- sometimes links are missing to changes, it is not possible to directly jump to them
• Mail
• Contacts
• Calendars
• Deck: Allows note-taking, hierarchical organization into deck -> board -> stack -> card
  • Card: has users, description, attachments, timeline, tags