Subversion is one of the most famous VCS (Version Control System) that supports both version control models; the copy-modify-merge and the lock-modify-unlock ones, and my favorite Subversion clients is called Work Bench; very user friendly and fast, the best one I’ve met till now and it’s available in the official Ubuntu repositories, here is how you can get it:

1. Open the terminal and type: “sudo apt-get install svn-workbench”
2. If you don’t find its launcher in Applications>Programming (in older versions of Ubuntu), you can run it directly from the terminal by typing “svn-workbench” or create a launcher in the menu by yourself by right clicking “Applications”>Edit Menus, select Programming and click “New Item”, customize the launcher as you wish, but you must fill in the field “Name” and “Command” at least, type “svn-workbench” in the “Command” field.