CVS stands for Concurrent Versions System and helps developers keep track of the current code base. The Atlas project uses CVS for managing the current development version of Atlas.
Anyone is free to check out (the same as download) the current development version from Atlas CVS archives - in fact, you are encouraged to do so, since you are likely to get more exciting features than if you download the latest released version (on the other hand, the CVS version might also contain a bug or two that is not in the released version).
To check out a new copy of Atlas from CVS, cd into the directory where you want the new Atlas directory to be created and run the commands listed below. When prompted for the password, just press the Enter key. The necessary commands are:
cvs login

cvs -z3 co Atlas

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