Git is a popular source revision control system. GitForce is a GUI front-end for the git command line tool and runs on both Windows and Linux. It is designed to be easy and intuitive to use and yet powerful enough so you don't need to use a command line git.
A simple CVS client that bypass any firewall blocking port 2401 used by cvs. It relies on the ViewCVS web interface to the repository to work. To use when all other solutions (SSH...) fail
TunnelTools is a set of perl scripts to allow anonymous rsync and CVS access from machines inside a firewall by tunneling over an ssh connection to a host outside the firewall.
Gruntspud is a graphical CVS client written in Java. It supports a variety of different connection mechanisms (local, pserver, ext, ssh & server). It is intended to be able to run as a plugin to jEdit but also as as a standalone application.