GNU arch 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.

GNU arch has some features that make it particularly useful for public free software projects:
- it's easy to learn
- it's inexpensive and easy to administer
- it's a distributed system so there's no need to give write permission to every project participant
- it has excellent support for the kinds of branching and merging that can make a free software project team shine.

Another goal of the arch project is to help free software development projects work better: migrating from CVS or another system to arch should help your project operate more effectively.

GNU Arch was created and written mainly by Tom Lord.