DAVx⁵★★★★★Background app that syncs your non-Google cloud accounts with your Android system calendars and contacts.
Feedly★★★☆☆Cloud-based feed reader with all the bells and whistles, focusing too much on the bells and whistles.
Firefox Sync★★★★☆Works on nearly every Firefox-based browser and can mix and match. Even IronFox and LibreWolf recommend using it, as it’s encrypted end-to-end.
Floccus Bookmarks Sync★★★★★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.
Nextcloud Bookmarks★★★★☆Online web app for managing bookmarks using your own Nextcloud server. I usually use it indirectly as the storage for syncing via Floccus.
Nextcloud News★★★★★Simple web-based news reader for Nextcloud, easy to install and syncs with multiple desktop and mobile clients.
Nextcloud Notes★★★★★Simpler than Google Keep, more private, with human-readable data that syncs quickly and cleanly with your devices.
Postmarks★★★★☆A self-hosted public bookmarks/linkblogging server (think Delicious or Pinboard) that can interact with Mastodon and the rest of the Fediverse.
Wayback Machine Browser Extension★★★★☆Useful for when you want to make sure the pages you’re reading will still be around in some form in the future, and to easily get at additional context. Checks every page you view against the Wayback Machine, so turn it off when you’re not using it.
Xmarks (Discontinued)★★★★☆Xmarks was a cross-browser bookmark sync service that I used for a long time to keep Chrome, Firefox, IE, and Safari on multiple computers using the same set of bookmarks. It shut down in 2018.