Free editable online world map. Use this tag whenever a primary requirement of your software request is using OpenStreetMap resources.
OpenStreetMap is a collaborative project to create a free editable map of the world – one could say "crowd-source map-creation". The project already features a comprehensible amount of resources, and there's plenty of software on most platforms making use of it: for web-mashups, navigation, and more. Find details on the project on the linked Wikipedia page as well as on the project's homepage.