OsmAnd is a mapping and navigation application built on OpenStreetMap data, with the defining characteristic that maps are downloaded to the device and rendering and routing happen locally rather than being requested as you travel.
That architecture is the whole argument for it, because the places where navigation matters most are frequently the places with the least coverage, and an application that fetches map tiles as it goes becomes useless at exactly the wrong moment. Downloading a region in advance means turn by turn guidance, search, and rerouting all continue with no connection at all, and the data is stored rather than cached so it does not expire when it is needed. Routing profiles cover driving, cycling, and walking, and they genuinely differ rather than being the same route with different timings, since a cycling route respects paths a car cannot use and a walking route ignores one way restrictions that do not apply. Lane guidance and speed limits are present where the underlying data includes them, which is the honest framing, since coverage and detail vary by region according to how thoroughly that area has been mapped by contributors. Local rendering also allows the display itself to be configured to a degree that server rendered maps cannot offer.
The interface carries the cost of that configurability and is considerably denser than the mainstream alternatives. Map downloads consume real storage, and a large region is a deliberate decision rather than something to do casually.
Link: OsmAnd on F-Droid