I had actually thought that with the advent of MacOS X, Apple had done away with font incompatibilities. It installs Windows and Linux fonts with no problem, so there’s no need to have your own font file format, right?
My wife discovered the .dfont file this morning at work. As of this writing, the Wikipedia entry on the format is just a stub.
Datafork TrueType is a font wrapper used on Apple Macintosh computers running Mac OS X. It is a TrueType suitcase with the resource map in the data fork, rather than the resource fork as had been the case in Mac OS 9. It uses the file extension .dfont.
In plain English, it’s got all your regular TTF information in a different part of the file. Kind of like a .ZIP file for fonts. Useful, except only Macs read it. Fortunately, we have fondu. It’s available for all Unix systems (including Mac OS X) and provides a suite of utilities to convert different formats of TrueType fonts.