AncientFS is a file system for MacFUSE that will mount all sorts of ancient file systems in the form of data containers as regular volumes on Mac OS X. "Examples of 'data containers' include file system disk images, tape images, incremental file system dumps, tape archives, and library archives." You may then browse these volumes through the Finder as if they were regular volumes. They are read-only, and will preserve as many aspects of the original file system as possible.
In addition, Singh also introduced support for file systems in the System V and UFS families, as well as support for MINIX' file system. When put in a single image, this shows what new file system capabilities Mac OS X gets through these new features of MacFUSE.
I don't know many of the ones in the 'ancient' category, but they do sound cool.