From this post on Ajaxian.com today, there's a look at a new PHP-based library/framework to help with Flash remoting - AMFPHP.

MFPHP is an open-source implementation of the Flash Remoting framework. It’s fast, reliable, 100% free and open-source. With this new version we have strived to make a product as stable and full-featured as ColdFusion-based remoting (the reference implementation).

You also get to use the wonderful NetConnection debugger, which shows you exactly what's being sent between the client and server. Remoting uses AMF, a very lightweight binary format that cuts the bulk out of packets, meaning data exchange is a lot faster than with XML.

You can get the complete details from their homepage or just dive right in to their documentation...