Livre d'Or

Have you played 0h h1? There are app versions as well as the web one. I find it intensely satisfying (usually on the 12x12 grid!) but have also been playing it a bit with my older nephews (6 and 4) - the older one can manage the 4x4 if he's concentrating and 6x6 with a bit of help; the younger can just about handle 4x4 but it's definitely work.