Examples

Hadoop, http://hadoop.apache.org/core: Hadoop is the most wide deployed open source software for cloud computing. Hadoop is deployed on all the nodes of the Open Cloud Testbed.
Thrift, http://incubator.apache.org/thrift/ : Thrift is a software framework for scalable cross-language services development. It integrates a software stack with a code generation engine to build services that work efficiently between C++, Java, Python, PHP, and Ruby. Thrift was developed at Facebook. Thrift is expected to be available shortly on the Open Cloud Testbed and will used to interoperate different cloud middleware and to simplify the development and deployment of cloud applications.

Open Cloud Computing Software