https://wiki.openstreetmap.org/wiki/MapSwipe

MapSwipe mapswipe.org is a mobile phone app and a web app developed by a team in collaboration with the Missing Maps Project as an easy way for people to contribute to humanitarian mapping efforts. The contribution is indirect. A form of “second level crowdsourcing”.

It is an open source tool developed (and continues to be delveloped!) by the multiple organizations and communities in collaboration with the Missing Maps Project.