Amongst others the following interfaces to standards of the Open Geospatial Consortium (OGC) are available: WMS, WFS, GML, KML and SOS (The layertype SOS is a development which can be traced back to an initiative by terrestris GmbH & Co. KG). Other formats supported by OpenLayers are: GoogleMaps, Bing Maps (formerly MS Virtual Earth), OpenStreetMap, ArcServer and also direct processing of data from interfaces like GeoJSON.
The OpenLayers architecture allows easy integration into any website without the need to set up a complex server environment. In addition OpenLayers has a neat object structure and a very dynamic developer- and user community.
In the year 2008 the project underwent the obligatory incubation process and since then is an officially registered project of the Open Source Geospatial Foundation (OSGeo). In conjunction with the incubation process a code-review by neutral third parties is mandatory and it was also checked whether it was legal to published all the code under the given license.
OpenLayers is available under the BSD-license. If you are interested in using OpenLayers or you are just curious how it works then we can also recommend the OpenLayers book (sorry, only in german).