Chess GUI that allows null-moves Is there a GUI that allows null-moves as legal moves? Of course for engines the null-move heuristic already is an established technique.
Fritz allows null move entry via CTL+ALT+0. There may also be a menu option to do this.

Scid vs PC also allows this by capturing one king with the other or by using the keyboard to enter "--" i.e. hit the minus key twice.

Hiarcs also uses king takes king to enter a null move. There is also a menu option "Insert/Null Move" in the "Edit" menu, plus a keyboard shortcut of CTL+0