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RainRadar is a nifty and simple viewer to display the meteorological rain radar maps of Germany since it has been started. It fetches the radar images from wetter.info, stores them internally and displays them as continuous looping (sort of) video.
A downloadable (and the most recent) version of Theia can be found here (in dist/rainradar.jar).
License: Creative Commons 4.0 BY SA NC
This program is distributed WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.