All of the sample apps listed here use the Flutter TabBarView class in an interesting way. The Sample App Catalog page lists all of the sample apps.
Any widget with a PreferredSize can appear at the bottom of an AppBar.
This app features the following classes: AppBar, PreferredSize, TabBarView, TabController.
An AppBar with a TabBar as its bottom widget.
This app features the following classes: AppBar, DefaultTabController, TabBar, Scaffold, TabBarView.