Wulala - Secure Online Storage Backup & Synchronize Files

Image representing Wuala as depicted in CrunchBaseImage via CrunchBaseWuala is a free secure online storage which allows its users to securely store, backup, and synchronize files across multi computers and operating systems(Windows, Mac, Linux). Wuala's servers currently in Germany, Switzerland, and France. You can share files easily with friends, groups, and the world. All data encrypted on your computer.

Users start with free 1 GB of storage but can get more by inviting friends to wuala(up to 3GB), trading idle disk space or by buying additional storage. Wuala comes as a client for Windows, Mac, and Linux. Start it, you'll get a network drive named WualaDrive like SDExplorer. If you close it, this drive will disappear.

Main interface of wuala client. Very simple, you can drag the files into it.
You can set the permissions of files or folders: Private, Public and Share. If you choose Share, you will get a public link of your file, then you can share with your friends - with no registration required.
The most special feature of wuala, if you want more storage or be a pro menmber, it's not necessarily to pay for it, you can trade with wuala with your local storage. 

Overall, I don't like its client very much, it's a bit complicated compared to Dropbox, and you can't manage documents from its website. But its security should be guaranteed.

Note: 1. Java is needed for installing wuala.  
          2. Trade local storage need your computer is online for at least 4h/day.