The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.

Cassandra was open sourced by Facebook in 2008, where it was designed by one of the authors of Dynamo. In a lot of ways you can think of Cassandra as Dynamo 2.0. Cassandra is in production use at Rackspace, Digg, and a number of other companies, but is still under heavy development.