OPML Creator is an open source OPML editor. It is written in C#. The codebase is broken up into two parts. The OPML_Creator class hierarchy which handles all the editing and handling of OPML files and the GUI which uses the classes. The GUI is a forms based implementation

Instead of working with the XML directly any imports are converted to class properties.

Current Releases:

Base Classes: 0.1
GUI: Not officially released.

It looks like this project has stalled.