OsmAnd! It can download vector maps for countries at a time so you can navigate offline. It's a bit janky sometimes but hey.
CityMapper uses OpenStreetMap data for the cycle and walking route planning (even though the GUI is Google Maps). Best cycling directions you can get, full stop. The algorithm is by CycleStreets, a UK academic start-up out of a university.
Maps.me is more user friendly than OsmAnd and feels more like Google Maps, but needs internet and just feels a bit strange to me. Ad supported but you can turn the ads off in the settings.
