In my travels of late Celeste has come up under several different circumstances. I'm going to attempt to collect a few details in a place to point people at and say how cool it is here, but in the end point you at the project.
Celeste is essentially a peer-to-peer storage system. It is highly-available and scalable due to it's peer-to-peer nature. It's often compared to Honeycomb, but there are some substantial differences. Honeycomb was targeted specifically at fixed-content storage. It's reliability was built around the use of the Reed-Solomon encoding. And there was a close coupling of data and metadata in Honeycomb (providing the same failure characteristics for both).
Celeste does split an 'object' into blocks which get dispersed into the Celeste storage 'cloud'. It is possible to specify the number of copies of each object that is stored in the system. Celeste is also an application on top of the Beehive framework, but I need to spend a bunch more time looking into that before I understand how these interrelate.
There's a good article talking to Glenn Scott about Celeste which goes into a lot more details than I've mentioned above.