another column-oriented database: Apache Cassandra

I came across an article at H-Open on Apache Cassandra. The Cassandra project was actually started by Facebook, but then open sourced and "donated" to Apache, and Facebook got a Gold Sponsor of Apache. The article also includes a hint on Google's BigTable. "Cassandra is used by a number of other companies, such as Cisco, Twitter, Digg and Rackspace."