In a recent post to his blog Devis Lucato introduces the "Inversion of Control" design pattern and shares an implementation he's created as an illustration - a Service Locator called Select.

[In a Service Locator] all the dependencies are provided by a builder, which serves as a registry of dependencies and/or service definitions. The service locator knows how to instantiate each dependency. Such service exposes methods like 'getMailer()', 'getLogger()' etc. A service locator centralises the configuration detailing classes and parameters involved on objects instantiations.

He includes some sample code showing the structure of a Select implementation using a "Mailer" identifier and definitions of the classes to load for it. He also includes a bit of documentation of the (simple) API you can use to work with the tool - setting namespaces, replacing class definitions, creating definitions and finding the resource associated with a definition (to name a few).