A version control system

GNU Arch 1 (also known as tla) is a revision control system, similar in
purpose to tools such as CVS, SCCS, and Subversion. It is used to keep track
of the changes made to a source tree and to help programmers combine and
otherwise manipulate changes made by multiple people or at different times.

TLA is a punning acronym that stands for either "true love, always" and "three
letter acronym".