Organic Maps fits sort of fits that description. It's powered by OpenStreetMaps. Easy to mark and save locations and tells you the distance between two or more.
But Avenza has a free tier and I like it better honestly. Much nicer/easier to create interest points. You can use their basemap or make your own in Qgis if you have any GIS skills or use any PDF that has geo info embedded like a usgs topo map.
You can find any usgs topo map for free from usgs and load that into Avenza easily.
If you're interested and this sounds like what you're looking for I can dig up some links.
I had to switch to Esri Field Maps for work so I haven't used Avenza since they implemented a ton of new features but I still have it on my phone because it's a good app.
I've been using Backcountry navigator for a few years now. works great, uses forest service maps and others. selectable downloadable areas and and a few more useful features including compass on map.