Zooko Wilcox-O'Hearn of the Tahoe-LAFS project (which aims to make "cloud computing" storage more secure and private) writes:
Tahoe-LAFS is a secure distributed storage system. All of the files
that you store in Tahoe-LAFS are automatically encrypted so that
nobody–not even the people who control the computers that store the
data–can read or alter your files without your consent. Remarkably,
the encryption doesn't get in the way when you want to share specific
files or specific directories with specific other people.
Therefore, Tahoe-LAFS is good for backing up your personal files,
accessing them over the Internet, and sharing them.
All of the source code is Free-as-in-Freedom.
We just released v1.8 of Tahoe-LAFS. What is new is that downloads are
faster and more fault-tolerant, and it supports non-ASCII characters
on Windows, and it works on Win64. You should care because you want to
retain control over your own data, but you're already storing a lot of
your data on remote servers, and you're going to continue doing that
more and more in the future.