A group of prominent cloud vendors has banded together behind an open source project that promises to make application services available across clouds. Zend Technologies, the supplier of the PHP scripting language, launched the Simple API project Tuesday, and IBM and Microsoft were among the first vendors to sign on.

"We're very excited to participate. This is a very important effort," said Vijay Rajagopalan, principal architect for Microsoft's interoperability strategy team, in an interview. Microsoft will supply the project with a PHP software development kit for its Azure cloud, which is due to become operative in the second half of November.

Simple API will seek to counteract the tendency of each cloud to have some proprietary parts, making it difficult for an application to work with services in more than one cloud at a time.

The Simple API is intended to provide a common API set from which developers may call application services, regardless of which cloud they reside in. Files generated by an application running in one cloud could be stored on Amazon's S3, Rackspace's Cloud Files, Nirvanix Storage Delivery Network, or Microsoft's Azure Windows blobs. Rackspace and Nirvanix are also members of the project.

Simple API will also provide access to cloud document storage services, such as Amazon's SimpleDB or Windows Azure's tables.

In addition, in its initial phase Simple API will also provide access to simple queue services, including Amazon Simple Queue Service, which moves messages between two remote computers ensuring delivery, and Windows Azure queues, a similar message-queuing service.

"We started this open source effort to deliver sets of APIs to enable the next generation of applications," said Andi Gutmans, CEO of Zend Technologies, in an interview. The next generation of applications will be able to make use of application services wherever they find them in the cloud, rather than being dependent on those immediately available. At the start, a limited number of cloud services are covered by the API, but Gutmans said open source development will ensure that Amazon's EC2 is included as well.