See the header of any source file for the full license text. There is a detailed DGN Library API Reference available. There is currently no tutorial style information on how to use the library, but the dgndump.c utility can serve as a limited example. The initial project is essentially complete, but I am interested in fixing bugs and adding minor features. There may be a followon project to add DGN writing support.
Improvements are welcome.
The most recently committed code is available in CVS from remotesensing.org . I have made extensive use of this library to assist reverse engineering the file format. GraphStore has a product called eCADLite that can be used in demo mode as a DGN viewer. Columbus is a free document viewer which includes DGN support. Safe Software's FME product has excellent DGN read and write support, and can be used as a standalone product, or FMEObjects acts as a library.