Another app, “Make a Celtic knot”, makes a simple Celtic knot merely by specifying its basic shape. This app goes one step further. You have to choose each part of the knot, and rotate it until it fits its neighbours. Once the knot is complete, it gets automatically coloured in. You can change this colour. You can add more knots to the pattern, coloured differently if you wish. The app is easy to use, but fun to figure out which parts you need, and turned which way, to get the effect you want. If you want to save the finished knot, use a screen capture app to save the screen.