We've seen how to implement streams and wrappers and had a hint of the new filter API in PHP 5. You can apply this knowledge to... Implement additional URL protocols (eg: LDAP) Virtual Filesystem Layers by hooking %opendir()% and %stat()% eg: transparent webdav access Write reusable filters You can do most of the above in PHP script too - we have user-space mappings for many of these features.