Apache Hadoop is an open source software, and is repackaged and distributed by vendors who offer enterprise support and additional applications to manage Hadoop. The following is the listing of popular commercial distributions:
Amazon Elastic MapReduce (http://aws.amazon.com/elasticmapreduce/)
Cloudera (http://www.cloudera.com/content/cloudera/en/home.html)
EMC PivotalHD (http://gopivotal.com/)
Hortonworks HDP (http://hortonworks.com/)
IBM BigInsights (http://www-01.ibm.com/software/data/infosphere/biginsights/)
MapR (http://mapr.com/)
Microsoft HDInsight (cloud: http://azure.microsoft.com/en-us/services/hdinsight/)