OsmAnd
OsmAnd (https://osmand.net/) is OpenStreetMaps Automated Navigation Directions
It is a mobile device app for offline maps and navigation.
Additionally, you can use OsmAnd as a part of the editing process to make changes and contributions to OSM.
There is also a 'cloud' version which means you can access your maps online at https://osmand.net/map/
OsmAnd the best mobile app I've encountered, and the best part is how open, free, and privacy respecting they are in their mission[1]
User Guide
Source Code
https://github.com/osmandapp/OsmAnd
This project aims at providing comfortable map viewing and navigation (routing) application for mobile devices. Particular stress lies with complete offline features (via pre-loaded offline map data) or economic internet usage. To get started, continue with the basic description below, then find more detail on our Welcome Wiki Pages, the Project Homepage, or the OpenStreetMap OsmAnd Wiki Page. You are welcome to discuss any question regarding the project at the Google group OsmAnd. Please do not use comments on wiki pages because it is rather difficult to find them
