TravelbyArt (free with one in-app purchase) is a unique iPhone app designed for seeing Paris through the eyes of some of the artists who worked there.
The app contains detailed looks at the lives of Ernest Hemingway, Edith Piaf and Pablo Picasso during their years in Paris. You'll be led to places like Hemingway's favorite eateries (many are still open) and where he lived. There are also photos and built-in maps, with a button to transfer to Apple Maps for directions.
All in all, the app contains 20 tours you can follow to absorb the life of these artists -- that's more than most other guides provide. Phone numbers are even provided so you can make reservations at restaurants and other tourist stops.