Recs.
Updated
SpecsUpdate
Pros
Pro Allows offline use
The application can be used online and maps can be downloaded for offline use with all main functionality present. When the application is first launched it requires downloading world base map (131MB), a rudimentary world map, and offers downloading a more detailed map per country or region. Great for situations when the signal is unreliable or when abroad, since you can use the app without having to consider roaming charges.
Pro Based around crowdsourced OpenStreetMap data
OSM provides a map editable by everyone; just like the web-based encyclopedia, Wikipedia.
Using a community edited map allows one to correct isses they encounter. Combined with the monthly turn around, these edits are added for navigation quickly.
Pro Free and open source with a completely optional paid version
The app has a fully-featured free and open-source version, with code available on GitHub. The only benefit to getting the paid version, except for supporting developers and further development of the application, is having access to new features one release sooner than the free version.
Pro Excellent general map viewing
Sometimes one needs more than just navigation, they have a need to view a map or specify a specific route. OsmAnd provides a very nice, detailed map. This can be good for seeing what is around you or showing a place you are talking about to a friend.
It also provides a means to add waypoints on the map which can be used to dictate a specific route (not simple enough to do routinely).