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.
I have an interesting history with this app. The developers let me look at it in August of 2014, but I rejected the review because a purchase was required to see anything in depth. There wasn't enough content in the free version for anyone to make an informed purchase decision. That issue is fixed now, and the Hemingway section is complete and available in the free app. If you want the other tours, it's a US$6.99 in-app purchase, which I think is reasonable given the uniqueness of the content. It's nice to see app developers be responsive and make the app better for customers.
If you're interested in art, literature and music, and planning a trip to Paris, I recommend TravelbyArt. I found it easy to use, loaded with information you will want to discover, and it's a fresh approach to travel. The in-app purchase also includes a restaurant guide linking to the lives of the artists.
I think the app should be universal to help in planning a trip to Paris, but you can run it on an iPad in 2x mode. TravelbyArt requires iOS 7 or later, and it worked smoothly on the latest iOS 8 beta.