http://www.straightrunning.com/XmingNotes/

Xming is the leading free unlimited X Window Server for Microsoft Windows (XP/2003/Vista). It is fully featured, light and fast, simple to install and because it is standalone native Microsoft Windows, easily transported [WWW]portable as a Pocket PC X server. It is totally secure when used with [WWW]SSH and optionally includes an enhanced PuTTY Link SSH client and a portable PuTTY replacement package.

Xming is cross-compiled on Linux for Microsoft Windows (32-bit x86), using [WWW]MinGW, mainly from the canonical [WWW]X.Org source code with my patches applied. It is kept current and secure with frequent updates from [WWW]X.Org, [WWW]XKB, [WWW]FreeType2, [WWW]Pthreads-Win32 and [WWW]Freedesktop Bugzilla.

When released Public Domain, Xming can be distributed and used without restriction as it is open source licensed, mostly [WWW]MIT/X11.