We are releasing a new project called SmartClientPHP ( SmartClient for PHP ) under LGPL license.
It is designed to help PHP programmers that use "SmartClient Ajax Ria System", allowing them to write SC code faster and making sure that your application will keep working, even if a new SmartClient version is out.
There are two versions, one for ZendFramework and other for PHP/other frameworks.
1. it provides access to only a tiny subset of the SmartClient API
2. it's slower (introduces needless server processing)
As far as server integration, on the SmartClient public wiki there is now a series of articles showing how to build PHP server code for RestDataSource that supports full CRUD, including AdvancedCriteria and transactional commits to a database (using the RedBean PHP library).
This can be found at wiki.smartclient.com, under Third Party Integration -> PHP Integration