BFS is filesystem used in SCO UnixWare systems. The UnixWare 7 manual says: The bfs filesystem type is a special-purpose filesystem. It contains all the stand-alone programs (such as unix) and all the text files necessary for boot procedures. Because the object of the bfs filesystem type is to allow quick and simple booting, bfs was designed as a contiguous flat filesystem. It is not intended to support general users. The only directory bfs supports is the root directory. Users can create only regular files; no directories or special files can be created in the bfs filesystem.
You can download the BFS filesystem driver for Linux from ftp://ftp.penguin.cz/pub/users/mhi/bfs/ directory. Extract patch file and patch your kernel (e.g. bzip2 -dc bfs-...-patch.bz2 | patch -p0 in the /usr/src/ directory). Current patch is only for 2.3.x kernels (I used 2.3.2, but it should work with other versions too). Then make dep and configure your kernel. You should see the BFS filesystem in "Filesystems" menu. If you don't see it, patch failed or you didn't say Yes to Prompt for development and/or incomplete code/drivers (or both).
You should be able to mount read/only any BFS filesystem by typing mount /dev/device /mnt -t bfs. If you don't have your own BFS filesystem, you can use my BFS floppy image from FTP directory. Please tell me whether it worked or not. It's very important for me.
If you were looking for BeOS filesystem (I call it BeFS) you should rather look at this page.