Sharp Serialization Library serializes and deserializes primitives, ArrayLists and Hashtables, compatible with PHP serialize(). Use it for SOAP/Web Services communications where Hashtables cannot be passed otherwise, or saving to a file readable by php.
phpBeans provides software and specifications for enabling n-tier development within PHP, such as the phpBeans Object Server, and interoperable with other languages as well. phpBeans can be downloaded from http://www.sitelliteforge.com/