A tiny animated virtual pet that is always active in your status bar.
Start off with an egg you can hatch and try to keep it happy.
Through a single notification you can feed it, clean up after it, and play with it.
There are multiple difficulty levels that make more or less needy.
This simple homage to the monochromatic 90's Tamagotchi games works everywhere your status bar is.
The best part is it doesn't affect your battery!

All the data needed for the status of the pet is stored quietly in the notification itself and with broadcast receivers instead of a background service there is no significant battery drain.