DGNLib is a Microstation DGN (ISFF) Reader.
Frank Warmerdam has implemented a Microstation DGN reading library on contract to Avenza Systems Inc., makers of MAPublisher. The library will be OpenSource (under my usual X/MIT license), portable and callable from C/C++. While it has been incorporated into my OGR Simple Features library, it is also be usable standalone with minimal overhead.
The dgnlib library, and this page of DGN related information are primarily hosted at http://dgnlib.maptools.org.