Any GUI that can handle this? Hexagon chess board

[hgm]

WinBoard cannot display 45-degree rotated boards now.

But you are right: if you don't care about a shear transformation, it can support the game now. You just have to consider the squares along the diagonal as neighbors, and along the anti-diagonal as non-neighbors. (Or the other way around.) Then each square has six neighbors.

You can use a drawing with distorted hexagons as board texture.

[Dirt]

In case anyone doesn't understand, one side would look like this:
[d]3PRNQB/3P2BK/3P1B1N/3P3R/3PPPPP/8/8/8 w - -
It would take an 11x11 board to show the entire game.

[hgm]

It does not work very well. The default pieces are too big:



Using font-based pieces, scaled to a smaller fraction of the square size than usually, and offsetting the background a bit towards the lower-right corner, works slightly better:

[Dirt]

Wonderful. It looks better than I expected.

[hgm]

Well, Sjaak II can probably be configured to play this. Coordinate notation will probably be completely different from what is usual in this game, though. (Although it is not clear to me what is usual here...)