Used the Guidepal apps on my recent visit to Europe, and they were great.
All the reviews of attractions/restaurants/etc are available offline which is great. The offline map is great; it also links with your GPS to show you where you are and what is nearby. Reviews were very detailed and informative. I was sitting in the Pantheon reading all about it...
Riiiiich about Rome City Travel Guide - GuidePal, v1.71