Organic Maps is fantastic. I particularly use it for hiking, and it's fantastic. It finds some amazing trails that I would otherwise never have gone to. Sometimes they can be challenging or overgrown, so you have to know what you're doing and be prepared to turn back if necessary, but I owe a lot of truly incredible experiences to this app.
It originates as a fork of Maps.me, from when Maps.me changed to closed source. Since then Organic Maps has grown to become a lot better than the project it originates from, at least according to my preferences.