HexGui is a modified version of the application GoGui, for the game Hex. It was created mainly to have a Windows version of the open source engine Six (originally a KDE-Application by Gábor Melis).
GoGui is a tool for Go programmers and players, to display Go game trees, save them in .sgf format, attach an engine and debug it (analyze mode). Also some smaller non-GUI tools like TwoGtp (test two engines against each other) are included. GoGui is an open source application, written in Java, by Markus Enzenberger.
In HexGui, some features were removed (e.g. "set up" a position), and tools like TwoGtp may be untested, but could quite easily be made working again.
Link: HexGui homepage
Note: There is also another program named HexGui and derived from GoGui. This program is the GUI that the authors of Mohex and Wolve recommend on their web page. It is available at http://webdocs.cs.ualberta.ca/~broderic/hex/