Projects using Cassandra
http://github.com/tjake/Lucandra Cassandra engine for Solr and Lucene search
http://github.com/jedisct1/scribe log directly to Cassandra from scribe
https://github.com/thobbs/flume-cassandra-plugin Cassandra plugin for Flume logging
https://github.com/flewton/flewton the extensible Netflow collector
https://github.com/ticktock/qsandra A Cassandra backed PersistenceAdapter for ActiveMQ
http://esper.codehaus.org/ A Cassandra backend for Esper CEP
Cassandra clients
See ClientOptions
Proprietary products
Acunu develops a Big Data storage stack including a modified version of Apache Cassandra