OpenSSH for Windows
The light-weight version.
The standard way for installing OpenSSH on Windows is by installing from the Cygwin project. Cygwin is a port of many FOSS tools to a Microsoft Windows environment. Cygwin is rather hefty and includes many tools. There is a project that installs only a minimal set of Cygwin so that you can run the OpenSSH server without having to install the full Cygwin.
There is also a nice article on how to configure it for public key authentication.