Hello!
I now installed ownCloud on my Debian running on a VM and use it through DavDroid (I also consider donating some money to the developers, see: I introduce: Free Software Donation Day)
Since the ownCloud client is available for download on F-Droid, I might even start putting some files in the cloud.
For security reasons synchronisations only works if I am in my local network.
Edit: Also synchronising calendar and contacts with Mozilla Thunderbird.