Launched in 2010, Leaflet is an open-source library of Javascript code for the creation of interactive web-based maps. It operates using .json geospatial data and map tiles from external sources (Leaflet provides no basemaps of its own). It has been used in commercial contexts as well as academic projects, and it has been under private, individual ownership since 2010. While Leaflet is not the only library of Javascript mapping functions, it stands out for its comparatively long history, extensive documentation, and wide base of contributors and volunteers.
At its most basic, Leaflet accommodates fairly static maps, which can feature .json geospatial data (point or coverage), image overlays, and basic layer manipulation. But because it is a code base rather than an application, its functionality is limited only by the functionality of Javascript itself—an adept programmer could integrate a timeline manipulation function, multimedia, interactive pop-up boxes, or other features to increase interactivity and dynamism.