The advantages of storing data in the cloud are many: ubiquitous access to data from multiple devices, social interaction and sharing with others on the web and no extra software to install.
ownCloud is the first and most ubiquitous FOSS solution to run on the server or computer of the user or on an internal company server -- giving the user the benefits of cloud computing and control of the data. ownCloud integrates with desktop applications so that the users has cloud features combined with the security and the good cost structure of in house file servers.
ownCloud is a very active open source project which was founded in 2010 and has seen enormous growth since than. The main features are syncing and sharing of file, encryption, calendar and contacts syncing, media player, photo gallery and more.