I have following problem:
3 people are working on the same Java project and want to share a workspace so we can all work together. Our computers are connected to a local network, but we want to share the workspace created in one computer.
Git is currently the standard tool to use in this case. There are others but I would recommend using it over anything else. It is also free.
After downloading and installing on each of your machines create a public repository to store the project.
Here is the getting started page: http://git-scm.com/book/en/v2/Getting-Started-About-Version-Control