On June 27th, 2014 Flickr disabled the HTTP API that was used by Downloadr. The last version of Downloadr was released on September 10th, 2009 and does not support Flickr's new API. So eight years after the first public release and almost five years after the last update, Downloadr ceased to work and will not be updated anymore. You may still download the setup file but you will not be able to make any API calls.
Downloadr had more than 15 000 authenticated users and at times over 200 000 queries per day. It grew far more successful than I could have ever imagined. Thanks to all of you.