If you use a Nextcloud server, there's a good collection of apps (some official, some third-party) that work with it. The ones I use:
Nextcloud - main app, does authentication, file access, optional auto-upload photos Nextcloud Notes - kind of like Google Keep, but simpler. (IIRC Carnet is more like Keep, and also open) Nextcloud Talk - instant messaging, supposedly can do voice but I've never used it for that Nextcloud News - RSS reader that syncs your feeds and read/unread through your Nextcloud server
Plus these apps that aren't Nextcloud-specific, but work with it and other sync methods:
OpenTasks - ToDo list (needs Dav5x to sync) DAVx5 - Syncs contacts, calendars and to-do items between any CalDav, CardDav or WebDav servers and your Android system, so you can access them with any local contacts or calendar app. (For instance: K-9 Mail can use contacts from my Google account and my Nextcloud account, and Simple Calendar can do the same with my calendars.) Floccus - Bookmarks manager that can sync across multiple desktop browsers and the mobile app, using any of several sync options including Nextcloud