Just donated $100 to the amazing Organic Maps project: Trackerless, fully offline, OSM based, open source mapping for Android/iOS. Great UX & routing, super fast & good coverage even of hiking paths, elevation lines & public transport layers...
From their website: "Organic Maps is one of a few applications nowadays that supports 100% of features without an active Internet connection. Install Organic Maps, download maps, throw away your SIM card (by the way, your operator constantly tracks you), and go for a weeklong trip on a single battery charge without any byte sent to the network."