rcs binary package in Ubuntu Bionic amd64

 The Revision Control System (RCS) manages multiple
 revisions of files. RCS automates the storing, retrieval,
 logging, identification, and merging of revisions. RCS is
 useful for text that is revised frequently, for example
 programs, documentation, graphics, papers, and form letters.
 .
 Note: this package contains certain general-purpose commands
 (such as merge or ident) which may used by other programs
 installed on your system.

Source package