When iPhone apps first became available I dreamt of a new type of digital guidebook. You would carry it in your iPhone and it would use the assorted features of your iPhone to be more helpful than paper guidebooks. It could be more up-to-date, released more often, and available per city.
The first attempts to do this were dreadful. By now, some years later, we've got the excellent TimeOut travel guide apps. I use the TimeOut Barcelona app often, even though I am not a tourist but a resident. Want to find a recommended cafe within a few minutes walk of your current location? It does that. Offline maps? It has that too. Reviewed restaurants, night life, museums, and hotels are all there.
At the time of writing there are TimeOut apps for 16 cities. I hope the model is widely copied.