DAVx5β β β β β Background app that syncs your non-Google cloud accounts with your Android system calendars and contacts.
Floccus Bookmarks Syncβ β β β β Very flexible, syncs across many different desktop browsers and mobile devices, and for privacy it can run on your own server or encrypted on another cloud service.
NewsFlashβ β β β β Clean, stable, fast, free, no-clutter and no-nonsense RSS/Atom newsfeed reader for Linux that optionally syncs with multiple services.
Nextcloud Newsβ β β β β Simple web-based news reader for Nextcloud, easy to install and syncs with mobile clients.
Nextcloud Notesβ β β β β Simpler than Google Keep, more private, with human-readable data that syncs quickly and cleanly with your devices.
OpenTasksβ β β β β Simple to-do list that works great with a Nextcloud server.
Thunderbird (Email and Calendar)β β β β β Stable, capable desktop email application, works well with multiple accounts including Gmail, Nextcloud, easy to set up and use but with advanced settings when you need them. FLOSS.