cvs?
 

What is CVS?

Concurrent Versions System

An easier way to find out is:
What is Google

;)

A more hands on description to CVS is 'bleeding edge'. When code is edited, it's placed in CVS, and you can choose to use that fresh untested code, or you can wait for a release where they usually get enough feedback to consider it somewhat more stable. CVS is live.

Cool