Prism Knot

Prism Knot is a path-drawing puzzle. Each colour has two dots on the grid; drag from one to the other to lay a glowing pipe between them. Pipes cannot cross each other. Join every pair and the level is won; the more of the board your pipes cover, the more stars you get, and three are only for a board with no empty square.

Three hundred levels grow from five-by-five boards to fifteen-by-fifteen, across six chapters. Every board is built around a complete answer, so each one can be finished, and each level was chosen from several candidate boards so the difficulty climbs steadily instead of jumping about: the first ones solve themselves, the last ones make you plan the order. From level twenty the board adds its own rules: walls to go around, ice that a pipe has to cross in a straight line, fog that lifts when a pipe passes next to it, bridges where one pipe can cross each way, padlocks that open only when their key colour is connected, and portals that carry a pipe from one side of the board to the other.

A full board and one stroke per colour are both worth extra points, and the difficulty adjusts itself a little to how you play the new levels. There is a daily challenge that is the same board for everyone that day, and an endless Zen mode with no limits. A finished board can be shared as a picture of the solved grid.

Hints lay one pipe exactly where it belongs, and the bridge and thaw tools get you past the harder pieces. Eight pipe skins, a daily streak and missions. It can be played entirely with a keyboard, every colour can carry a symbol for colour-blind play, and it comes in eight languages. Progress stays in your browser.