StreetComplete makes contributing to OpenStreetMap easy and fun by turning contributions into “quests” on a map for you to complete. No personal information is required, just create an OpenStreetMap account, and start contributing directly in your area!
I tried this out myself, and it is truly fantastic! I had never heard of it, and I’m sure many of you haven’t either, so spread the word!
Tip: When entering buildings to ask questions (opening hours, etc.) be ready to explain what OpenStreetMap is :)
Taking a quick look at the source code, it seems like they use map libre for displaying the map which is open source. The only thing not open source are the JawgMaps servers, which serve the tiles for the map in the app. This means that there are no closed source libraries running in the app/on your phone, the only thing happening is the app sending HTTP requests to JawgMaps to load tiles.