Or there is Locus Map (for Android only), another great app from Czechia. I wonder what is going on in that country :) One ability of it that I find awesome is

Or there is Locus Map (for Android only), another great app from Czechia. I wonder what is going on in that country :) One ability of it that I find awesome is that there is a huge variety of online map sources, for example, in my home country there is an independent mapping project for hiking trails, and the maps are usually more detailed and better quality than OSM. I can easily switch to those maps when needed, and of course download them for offline use - but not the full dataset, instead you can draw a polygon of map boundaries that you want to have offline.