Half the apps on the Internet are written in PHP. That gives Zend Technologies, the PHP house, a stake in the cloud.

So it’s rounded up cloud merchants Microsoft, IBM, Rackspace, GoGrid and Nirvanix and has gotten them to support its new open source drive to create a so-called Simple API for Cloud Application Services that developers can write to – or, Zend thinks as likely, rewrite to – to get native cloud apps.

These apps in turn promise to break the lock on closed clouds like Amazon’s, making it possible to move applications and their data in and out of clouds, migrating them around virtually all the major nebulae.

The trick will be in creating Simple Cloud API adapters.

Zend cloud strategist Wil Sinclair – that’s right, Wil – says both Amazon and Google were asked to join the initiative.

Google’s widgetry is based on Python so it’s got an excuse for not joining. Anyway, the in-house Google Data Liberation Front is at least promising to cut the shackles that condemn captive users to remain customers of Google services because their data is held hostage like it already has with Google App Engine.

Amazon, on the other hand, reportedly sent Zend its best wishes but said it wouldn’t contribute to the effort.

Absent any Amazon contributions, the Simple API is still supposed to include interfaces for Amazon file storage (S3), document database (SimpleDB) and queue services (SQS).

See, the idea is to give developers a single API to interact with a variety of cloud application services without having to change their source code.

It’s unclear how deep IBM’s support will run or even what cloud IBM has in mind when the company’s cloud CTO Kristof Kloeckner says in a canned statement, “IBM will be contributing adapters for IBM’s cloud service interfaces as well as adapters to IBM’s data storage products, allowing developers to easily switch between public clouds, private clouds and traditional data center environments.”

Microsoft, whose Azure cloud has yet to go gold, is promising to kick in Azure interfaces for Azure blobs, Azure tables and Azure queues as well as PHP client libraries for Azure storage that provide transaction and partial upload support.

Ditto the storage services under Nirvanix Storage Delivery Network and the Rackspace Cloud Files.

Zend says it will also have adapters for local services to make offline coding and testing against cloud services “as easy as connected development.”

The adapters for Rackspace’s Cloud Files API are supposed to work with external libraries with no changes to application code.

Zend CEO Andi Gutmans says lack of portability has deterred cloud computing. Zend stands to benefit from the API because it will encourage use of the Zend Framework, where it will be a new component called Zend Cloud that uses existing client libraries.

However, it’s also supposed to translate to any object-oriented language for the web.

Zend’s posted an initial Simple Cloud API proposal and reference implementation at www.simplecloudapi.org. It says developers can evaluate the thing by deploying apps that use it on Amazon complements of the free Community Edition Zend Server Amazon Machine Image (AMI) for EC2. There’s also a commercial, supported version. A technology preview of the Azure PHP client libraries is at http://framework.zend.com/Zend Service WindowsAzure.

Zend, which started reaching out to vendors in April, fancies it’s good at creating communities. Wil imagines the initial discussion focused on what the cloud should be like.