Zuza B&B for Android
Free comprehensive tourist guide with offline map, lots of background info and pictures, which dynamically updates/shows relevant points of interest that are nearby, including their walking distance, taking into account your location and (optional) filter which you can modify. Very nice, and free as well! I am impressed.
Simple to use with info available offline too.
How did we survive before such apps existed?
by R####:
It really is a great guide in Lisbon, you don't need Internet to use it and it tells you were you are and what is around you. We used more than the lonely Planet book we had.