There are very few SSH client options available for the Microsoft Windows platform. Since the operating system comes without built-in SSH client and server support, users have had to build alternatives to interact with UNIX-based systems running SSH. Using platforms like Cygwin, users have been able to run versions of OpenSSH on Windows as if it were native, even though OpenSSH does not support the Windows platform.
PuTTY has become the most popular, graphical terminal services client for the Microsoft platform. PuTTY offers a wide range of features including built-in support for SSH tunnels. WinSCP, one of its sister programs, supports sftp as well. Supporting both SSH-1 and SSH-2 standards along with telnet, PuTTY is about as versatile a client as any Windows user could ask for on their platform. PuTTY can also be run off a USB drive as it comes as a binary when downloaded. It has grown to become the standard for users new to SSH who use a Windows platform.
OpenSSH on Cygwin
Cygwin is a Linux-like environment for Windows that allows Windows user to interact with some command line interfaced applications from the Linux application pool. One of the applications that runs well is OpenSSH, the free SSH client and server suite that comes bundled with many Linux distributions. Originally it was a hassle to install OpenSSH and Cygwin on Windows, but now an installable package is available that takes the hassle out of the install (see "Resources" below). While not as graphical as PuTTY, OpenSSH provides as close to a Linux-like environment as a Windows user could hope for. It is good for those looking to emulate a console environment that they are already used to and who know how to, and need to, use OpenSSH's powerful features.
Other, less-popular SSH clients exist for the Windows platform, but few are actually used. Clients like SecureCRT charge for their client and provide decent terminal emulation while others, like privateshell, just offer a more easy to interact with interface. Since most clients contain all the features of SSH, client preference and ease of use for users is a primary factor.