OpenLayers is a pure JavaScript library for displaying map data in most
modern web browsers, with no server-side dependencies. OpenLayers implements
a JavaScript API for building rich web-based geographic applications,
similar to the Google Maps and MSN Virtual Earth APIs, with one important
difference -- OpenLayers is Free Software, developed for and by the Open
Source software community.
Furthermore, OpenLayers implements industry-standard methods for geographic
data access, such as the OpenGIS Consortium's Web Mapping Service (WMS) and
Web Feature Service (WFS) protocols. Under the hood, OpenLayers is written
in object-oriented JavaScript, using components from Prototype.js and the
Rico library. The OpenLayers code base already has hundreds of unit tests,
via the Test.AnotherWay framework.