As you may know, Canonical has terminated Ubuntu One last year because they considered that the company is engaged in too many projects already and they can’t compete with Google Drive or Dropbox.
Today, the Ubuntu developers have announced that they have open-sourced a big part of Ubuntu One, permitting everybody to fork it and build a new cloud based storage service. The source code is available here.
The software is released under AGPLv3 open-source license.