The news page from the project's site details the changes.
For the uninitiated it is an container for components that follow the Inversion of Control and Dependency Injection principles. When it first started as a project in 2003, it was the only container that did the auto wiring of Constructor Injection. There are plenty of choices in this field these days, but PicoContainer is still used inside Intellij IDEA and JIRA.
Also using PicoContainer: Waffle is a Rails "convention over configuration" inspired web framework that some suggest is a deal more pleasant to develop with than Struts/WebWork.