A number of us are pretty happy with the Citymapper app.
From the description it looks like Citymapper is a transportation info & options app, if I'm interpreting it right.
GPSmycity seems to have more touring information. Its description:
"Thousands of self-guided walking tours, travel articles, and offline city maps. The app turns your mobile device into a personal tour guide using its built-in GPS functions. The walking tours and travel articles will guide you to the landmarks, historical sites, museums, restaurants, nightlife venues and other interesting spots in the destinations."