As far as it is possible to tell, this site is for an empty homes campaign in German-speaking Europe, most obviously Germany and Austria. It is reminiscent of the now-defunct report-an-empty site once managed by EHA.
If you have good German, feel free to give us more detail via the comment system.
The "About" link is hard to find. This seems to be it, but it is Hamburg specifc:
This is what Google Translate makes of it: