Merkaartor is described as 'OpenStreetMap editor for Unix, Windows and Mac OSX (prerelease, Intel only), distributed under the GNU General Public License' and is an app in the Travel & Location category. There are seven alternatives to Merkaartor for a variety of platforms, including Android, Android Tablet, Windows, Linux and Online / Web-based. The best alternative is StreetComplete, which is both free and Open Source. Other great apps like Merkaartor are JOSM (Free, Open Source), iD (Free, Open Source), Vespucci (Free, Open Source) and Osmosis (Free).
Vespucci is the first OpenStreetMap editor for Android, Codename "Vespucci", continuously improved and developed since 2009. It supports the full OpenStreetMap data model including lots of less known quirks and can be used, if necessary, completely offline.
The Openstreetmap Contributor app allows anyone to contribute to OSM. It enables those-who-know to easily manage a group of newbies as the contribution process is intuitive and easy. Bring your MapParties to a whole new level!.