Prioritize is a simple Sandstorm app to help keep track of periodic tasks which have some flexibility. Examples: misc. cleaning tasks, but also things like getting some exercise.
You add tasks with a "period" in days. The app then lists tasks sorted by how overdue they are, and you can mark them as "done," at which point they are removed from the list until their period has elapsed again.
This can be better than to-do apps where tasks just have fixed deadlines; it's great for organizing tasks that sometime slip by a day or two.