Think of it as Facebook Messanger for your todos.

When you got notification it will be showed in bubble over other appications.

Get reminder over other apps.
Notifications are easly sortable with drag and drop.
Many repeat options.
You could hide some notifications when time of task passed. It will be showed next day.
Subtask are also supported for reminders (from edit reminder).

*app is not releated to Facebook. It is opensource and code could be found at https://bitbucket.org/senpl/android-popup-reminder