ownCloud is a free software suite, written in PHP, that provides file storage, synchronization, and sharing. It provides the same basic features of Dropbox or Box.net. It also provides a whole lot more.
ownCloud was started three years ago when Frank Karlitschek wanted a free software alternative to proprietary solutions. In the time since the project has attracted a dedicated group of core contributors, made several significant releases, and is available in 42 languages. It’s also spun off a commercial project to drive development of ownCloud for enterprise users.