Darcs is a free, open source source code management system.

Darcs is easy to learn and efficient to use because it asks you questions in response to simple commands, giving you choices in your work flow.

You can choose to record one change in a file, while ignoring another. As you update from upstream, you can review each patch name, even the full "diff" for interesting patches.

Originally developed by physicist David Roundy, Darcs is based on a unique algebra of patches.

This feature lets you respond to changing demands in ways that would otherwise not be possible.