Gravity Tunnel

Gravity Tunnel is a browser space-tube runner. Your runner moves forward on their own; you jump and drift. The tunnel is a square tube and every few seconds the whole tube rotates 90 degrees, so the wall beside you becomes the floor under your feet — each of the four surfaces keeps its own layout of gaps, blocks and crystals. A black gap under your feet ends the run unless you are mid-jump; grey blocks kill unless you jump over or drift past them; teal crystals are worth 15 points each and distance in metres is the rest of your score. You start at 3.4 units per second and gain 0.02 per metre up to 7.5, so the tube gets seriously twitchy past 150 m. Rotations are scheduled every 3.4 to 5.5 seconds and the game never rotates you onto a surface with a gap in the landing stretch, so a switch is never an instant death — but what you do in the next second is up to you.