Plink (PuTTY Link) is a free and open-source (MIT license) command-line network connection tool similar to UNIX ssh written by Simon Tatham, author of another popular terminal emulator, serial console and network file transfer application name PuTTY It is mostly used for automated operations, such as making CVS access a repository on a remote server.
RapidSVN doesn't come with an SSH client so the user must install a client, for example the plink.exe that comes with PuTTY.