It's a distribution of the XWin server, a version of Xorg's X-Window server developed by the people of Cygwin/X. Basically, it allows you to start a X-server to access an xdmcp-enabled host or to launch remote applications. It's main advantage over the Xwin server distributed by cygwin is that you don't have to install cygwin, just download the 2Mb installer and you get a fully-fledged Xserver. This version is the first release on CNET Download.com.