They could have chosen a better name but here's the description. But it too sounds like it would need work because it mentions "WeirdX supports core protocols of X11R6.3 partially."

Open Source - WeirdX

written in Java

  * WeirdX handles x protocols directly.
  * WeirdX supports core protocols of X11R6.3 partially.
  * WeirdX is implemented with JDK 1.1.
  * WeirdX runs as an application/applet.
  * WeirdX supports Rootless mode.
  * WeirdX runs as a TrueType font X Server if your JVM supports
    TrueType fonts.
  * WeirdX supports the three mouse button emulation.
  * WeirdX supports copy/paste operations between the native
    window system and x clients via CUT_BUFFER0.
  * WeirdX supports 1bpp, 8bpp and 16bpp mode.
  * WeirdX supports multibyte characters; Japanese, Korean and
    Chinese characters.
  * WeirdX allows you to get secure X accesses in pure Java by
    using JSch.
  * JRexec is included.
  * WeirdX supports XDMCP.
  * WeirdX supports dxpc(Differential X Protocol Compressor) with
    the assistance of JDxpc.
  * WeirdX includes hacks for the alpha transparency.
  * WeirdX supports EsounD compatible applications.
  * WeirdX includes the XJS Extension written by Christian Werner.
  * WeirdX is distributed under GNU GPL.

<snip> There are a couple of java X Servers but I would be concerned about

On Wed, 2010-10-27 at 16:26 -0400, brian mullan wrote: performance. This is not an area of expertise for me but I would imagine we push the X Server rather hard. If cygwin struggles simply because the network stack is shimmed, I would think the java overhead would be crippling. Just a hunch - John