The task-list feature in Evolution (GNOME's email client) defaults to showing both complete and incomplete tasks. There's a built-in filter to show only complete tasks, and one to show "active" tasks (whatever that means; apparently I have no active tasks), but apparently no option for "show me the list of things I need to do", so I added it myself as a custom search.
Evolution doesn't bother to remember when custom searches are active, so every time I switch back to the "task" view, I have to choose it from the searches menu again.
I get the distinct impression this feature is designed for a use-case I don't have, not for basic to-do tracking.
OK, GNOME also includes an app called "gnome-todo" that reads the same task database (so all my tasks are already there), but (a) it defaults to hiding completed tasks, and (b) there's menu option for "clear all completed tasks" so right there that's a dramatic workflow improvement.