Drag a finger across a dark screen. A glowing trail follows it and fades behind you, and the phone answers with small distinct taps that keep pace with your hand. Move slowly and the taps space out. Move quickly and they tighten up toward a rapid patter. Stop moving, and it goes quiet. Lift your finger and it stops immediately. That is the whole app. WHAT IT IS NOT No account. No sign in. No streaks, no daily goal. No timer counting your session. No notifications asking you to come back…