K-DBX is based on LibDBX (part of the ol2mbox project), and is able to load Outlook Express files and display their contents. If K-DBX loads the "folder.dbx" file, then it will display the folder structure as a tree on the left, allowing you to click on a folder to view its contents.
LibDBX, part of the ol2mbox project, contains C and a C++ interfaces for accessing Outlook Express dbx files. The C++ interface is just a wrapper for the C interface. It includes two programs. One will read a dbx file and output the emails in mbox format to stdout, the other will read the main "folder.dbx" file and export all the folders into separate mbox files.