We mostly talk of general-purpose file systems
But systems frequently have may file systems, some general- and some special- purpose
Consider Solaris has
tmpfs – memory-based volatile FS for fast, temporary I/O
objfs – interface into kernel memory to get kernel symbols for debugging
ctfs – contract file system for managing daemons
lofs – loopback file system allows one FS to be accessed in place of another
procfs – kernel interface to process structures
ufs, zfs – general purpose file systems