RCS (Revision Control System) is very useful for small groups wanting to operate on and update common files. It provides a way to "lock" files while changes are made and provides a method to document why changes where made.
For the best explanation see the man page:
That is the best place to get an overview.
Typical use will be something like:
co -l filename # check out file from RCS with a lock # vi/edit filename (make changes) ci -m"I made this change" filename # check file back in to RCS to remove lock... provide a message to explain changes co filename # after you do "ci" it won't be in present directory anymore, check it out without a lock
For groups wanting to share files, we recommend the directory with the files and RCS directory within have 2770 permissions for the group
Useful tools include rcsdiff (show differences between different versions) and rcslog (describes changes made)
For more information see more of the man pages or many of the hundreds of pages available via Google.