One of the big hurdles for an enterprise to move to the cloud is the fear of getting locked into a specific cloud implementation. This is one of the big reasons apart from security of data that keeps most of the enterprises out of the cloud space. Currently each vendor provides their unique set of API to interact with their Cloud services. This mandates a need to recode and refactor when moving from one cloud provider to the other.
jClouds is a multi cloud framework which allows connection to multiple clouds such as Amazon, VMWare, Azure, and Rackspace. jClouds provides portable abstractions for cloud specific features, thus allowing the application to move from one cloud vendor to the other with relative ease. jClouds also had a simulators to operate in restricted environments like Google App Engine and Android. Unit testing and mocking is made easy through stub connections which simulate the cloud.