I would say something like Git might fit the bill:
- As it’s a distributed system, you don’t need to have a central repository, the repos exist with the source directory
- It is easy to create patch files that can be mailed and applied.
- Although it might seem that git is difficult to use, the basic ideas of committing, merging, adding and removing files are not that hard to learn.
Have a look at this site Git Magic
or, even this tip site GitReady