Productivity
Notesnook
End-to-end encrypted notes app with open-source clients and sync across all platforms.
Brax recommends
Encrypted, cross-platform notes for users who want a modern Evernote replacement.
Notesnook encrypts notes, attachments, and tags with per-note keys and offers a generous free tier. The server is currently source-available rather than fully open, but the roadmap is public and active.