The Core project is geared towards the fundamental functionality of PicoContainer
The Gems project contains value-added Injectors, Containers, Monitors, and Parameters that often require additional dependencies to support each behavior.
Note: Pico-Gems is designed so that you need to only import the dependencies needed for a given feature you need. For example, CommonsLoggingComponentMonitor only requires the Apache Commons Logging project. You don't have to import the Servlet API to use it.
The TCK is a test suite to allow you to create and verify your own MutablePicoContainer-based solutions.