JOSM is described as 'extensible editor for OpenStreetMap (OSM), written in Java' and is a Map Service in the Travel & Location category. There are eight alternatives to JOSM for a variety of platforms, including Online / Web-based, Android, Android Tablet, Windows and Linux. The best alternative is StreetComplete, which is both free and Open Source. Other great apps like JOSM are iD (Free, Open Source), Vespucci (Free, Open Source), MapComplete (Free, Open Source) and Potlatch (Free, Open Source).
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.
MapComplete is an OpenStreetMap viewer and editor. It shows map features on a certain topic, and allows to see, edit and add new features to the map. It can be seen as a webversion crossover of StreetComplete and MapContrib.
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!.