Linux, Unix, Solaris. Linux supports SSH. To connect using SSH, see the "Tunneling Using Cygwin" section below.
In important regards, procedures for tunneling with a Mac client terminal resemble those for Windows clients. Mac users can download and install any number of free or for-fee terminals, the most popular being MacSSH, which is characteristically easy to use, is free, and offers superior performance for SSH1 connections.
NiftyTelnet 1.1 SSH, a fast and easy-to-use telnet and SSH1 client is also free. It supports effortless scp (secure copying), as well.
Mac OS X, based on FreeBSD and the Mach 3 kernel, has SSH built in and is constantly updated. You can also obtain and use F-Secure SSH, to create a desktop terminal allowing you to tunnel to the CVS server. For SSH1, you will want F-Secure SSH v.1.02; v.2.1 is for SSH2 connections only--i.e., those requiring encrypted certificates, or keys.
If you are using Windows (NT or 9x or 2K), then you can use SecureCRT, F-Secure SSH, or Cygwin. Cygwin, from Cygnus Solutions, provides a nearly full Unix environment on your desktop.
In contrast, SecureCRT and F-Secure SSH only provide user-friendly terminals, i.e., they don't pretend to emulate a Unix environment. Both F-Secure SSH and SecureCRT cost money ($100 for SecureCRT, $150 for F-Secure SSH), although a free, 30-day trial version is available for each. Of all, Cygwin has the added value of not just being free and very powerful, but also open source and constantly improved upon.