Are there any open source,
PHP based, role based access control system that can be used for
What I can tell you, however, is the Zend_ACL component of the Zend Framework will do role-based setups (however you'll have to subclass to check multiple roles at once). Granted the pain of this is you'll have to pull out Zend_ACL, I do not believe it has any external dependencies, from the monolithic download (or SVN checkout).
The nice thing about Zend_ACL is though its storage agnostic. You can either rebuild it every time or it's designed to be serialized (I use a combination of both, serialize for the cache and rebuild from the DB).
Maybe I'm misunderstanding the question, but isn't the whole point of Role-Based Access Control (RBAC) to avoid Access Control Lists (ACLs)?
RBAC differs from access control lists (ACLs) (...) in that it assigns permissions to specific operations with meaning in the organization, rather than to low level data objects. For example, an access control list could be used to grant or deny write access to a particular system file, but it would not say in what ways that file could be changed. In an RBAC-based system an operation might be to create a 'credit account' transaction in a financial application (...). The assignment of permission to perform a particular operation is meaningful, because the operations are fine grained and themselves have meaning within the application. (Quote: Wikipedia)
I don't know the specifics on Zend_ACL or the other implementations mentioned, but if they are ACL-based, I would not recommend using them for role-based authorization.