The Exchange 2016 Preview is now available for download:
http://www.microsoft.com/en-us/download/details.aspx?id=48210
The preview is currently only available in English and is just under 1.7 GB in size. The preview even supports co-existence with Exchange 2013 and Exchange 2010.
More information about the new features can be found on the Exchange Team Blog:
http://blogs.technet.com/b/exchange/archive/2015/07/22/announcing-exchange-server-2016-preview.aspx
Documentation is also already available on Technet:
https://technet.microsoft.com/library/mt170645(v=exchg.160).aspx
The download could be a bit faster though... 
Update: The setup is already in German.
