Say i have a unity project with 4 scenes called scene1.unity scene2.unity… to scene4.unity, and i want to distribute the project into 4 similar files for 4 developers so that they can all work on it at the same time. They edit 1 scene each and send back the project. What is the best way to divide and recombine the game into one?
Hi, you should use a version control system. Do you all have Unity pro ?
If yes you can enable meta files and you will be able to share the project between the co worker using SVN / TFS or other version control system.
http://docs.unity3d.com/Documentation/Manual/ExternalVersionControlSystemSupport.html
You can also purchase the Team license which is the Unity built-in version control system.
Enable “external version control” in the editor settings, and then preferably use a decent source control system to distribute the project.
If you really don’t want to use a proper source control system then you can just send the “Assets” and “ProjectSettings” folders to the other developers, and have them send them back later. Then you need to figure out which files each developer changed, make sure they don’t conflict, and merge them together. If they are strictly working on separate scenes then this might not cause a problem, but you might see some files in ProjectSettings conflicting.
If you have pro then enabling text-based serialization can also help when you need to merge things or understand exactly what a developer changed in a scene or prefab file.
The Pro text based merging is useless when multiple people working on it. use prefabs as your best way to multiple people working on the same scene
Meta file support is now also available in the free version with (?? 3.5 or 3.4)
1 - Enable Meta files
2 - Setup a https://bitbucket.org/ account or other free/paid server (github)
3 - Read up on Version Control (general) + the available systems (svn / git / mercurial / etc)
4 - Create a repro invite your people etc.
5 - Make sure that the individuals only work on there own scenes and that they do not change prefabs.
6 - Realize that this works okayish
7 - Buy asset server Team license 
How does the Asset Server Team License work? The main page does not discuss much workflow information.