EIEIO contains the core object library for CEDET. You can define classes, and methods for those classes using CLOS style syntax. Objects can be customized using the Emacs customization tool, which allows easy creation of dialog box style UIs. A series of base classes allows the creation of Emacs centric tools, wrapping up the details of persistence, instance tracking, or instance inheritance.
EIEIO also includes an example tool, chart.el for drawing simple charts.
Lastly, EIEIO has baseclasses for writing Speedbar interfaces. Take an existing object hierarchy and inherit from these baseclasses to be browsable in Speedbar.
For more details on EIEIO, read the see EIEIO Reference Manul.