I manage a team of 4 developers, working on several projects at the same time, some working on the same project.
Work is assigned so each person develops a different module of the system. This way, they can work without worrying the other person could mess his code.
However, the problem arises when we it’s the time to integrate and test the full system, and send it to production environment.
The solution for this is to use a “Source Code Control” system.
There are several options: some free, open source, proprietary solutions.
Given we work developing for the .Net platform, some tools I’ve seen are Visual Source Safe and Visual Studio Team Foundation Server.
On the open source side, I’ve seen Subversion, Git and Mercurial.
Finally, I decided using Subversion, because it was easy to install and start using, specially after reading this post, which is my main reference.