CDH is Cloudera's distribution of Apache Hadoop and related projects, shipped inside Cloudera Express. All components are open source (Apache License); see Release Notes here. (To see packaging info for the CDH 5.0.0 Beta, click here.)
Cloudera Express offers the best automated, all-in-one install experience for all cluster sizes. For a single-node desktop sandbox environment, install Cloudera QuickStart VM.
Cloudera Standard will provide the best all-in-one install experience for all cluster sizes. But if you're a Hadoop hacker who wants to install CDH components individually as Linux packages, click here for instructions.