Software Management

Is there software specifically for unity that manages game versions and updates made by programmers?

If so, what is it?, is it free? and where do I get it?

If not, what do people recommend?

I ask because I have team members scattered around the world and managing/re-distributing their contributions is becoming difficult.

Unity’s own Asset Server is designed for that, but it costs you. Other than that, use SVN or GitHub, and be sure to follow this: http://docs.unity3d.com/Documentation/Manual/ExternalVersionControlSystemSupport.html