MapProxy is an open source proxy for geospatial data. It caches, accelerates and transforms data from existing map servers. Unlike other solutions, the OGC WMS standard remains on client and server-side.
It acts as a middle-man between existing WMS servers (like MapServer or GeoServer) and WMS clients. All existing web and desktop GIS applications can be used, but also modern clients like OpenLayers or GoogleEarth.
Go to http://mapproxy.org for more information.
The documentation is available at: http://mapproxy.org/docs/latest/