Other people have already written that it's a fork of OrganicMaps by original authors.
I'll just add that for me OrganicMaps is much better than current Maps.me which is getting worse and worse after it was sold to some Korean (or Chinese, don't remember now) company.
The UI is much simpler and in recent months you can really start to see that OrganicMaps is becoming more detailed. I used to check from time to time the difference between Maps.me and OM and and it used to not be much of a difference, but now you have: more POIs (point of interests, like physiotherapist, specific kind of shops, etc.), better rendering of walls, fences, cliffs, embankments, hedges, better rendering of parking places (very recent update!), and more!
