I come from a MS / C# / .Net background, and am accustomed to everything that the .Net Framework has to offer, including WCF. When building a service tier in .Net, the choice of what framework to use is easy: WCF. WCF gives you the ability to write something once, and the flexibility to expose that functionality in multiple ways and in a variety of serialization tactics using only a configuration change.
As a newcomer to PHP, I'm trying to determine what libraries / APIs / frameworks in PHP can rival what WCF has to offer. What is the best library / API / framework / approach to use when beginning to construct a service tier in PHP? Is there anything that can do what WCF does in PHP?