Apache Cassandra is a database used by Facebook. It has converging databases. If you're used to normal SQL databases, it would be like a way of replicating information across lots of copies. Updates are done in really strange ways. Imagine a Facebook comment or status update. That gets a time associated with the data, and the database copies slowly converge to a common truth.
> gets a time associated with the data
it's easy to fake a timestamp in an untrusted network.