TRAIL is a long-exposure camera app for Android. The user points the phone at moving light and taps a shutter; the app continuously reads frames from the device camera and stacks them into a single accumulated image that builds up live on screen. Five capture modes, each a different way of combining frames: Light Trails (keeps the brightest value each pixel ever had, so headlights become continuous ribbons), Comet (the same but trails fade behind the light), Silk (a running average, so waterfalls and waves smooth into one flow), Light Painting (only pixels above a brightness threshold accumulate, so a torch waved in the air draws a glowing line on an otherwise unchanged scene), and Motion Art (an exponential moving average producing soft ghosting of people in motion). The user can adjust brightness, tail length, trail thickness, light threshold, frame ratio (3:4, 9:16, 1:1) and choose from 8 colour looks. Results are saved into an in-app gallery and can be shared through the Android share sheet. Pro users can also save a video of the exposure building up. ALL IMAGE PROCESSING HAPPENS ON THE DEVICE, in the phone's GPU via WebGL2. Camera frames are never uploaded, never sent to any server, and never leave the phone. There is no user account, no sign-up, no login, and no advertising SDK of any kind. Monetization: freemium with subscriptions through Google Play Billing. The free tier gives the Light Trails mode with exposures capped at 15 seconds, reduced-resolution export with a small watermark, and a gallery limited to 12 items. TRAIL Pro is sold as a weekly subscription and a yearly subscription (each with a 3-day free trial) and as a one-time lifetime purchase. Pro unlocks all five modes, removes the exposure time limit, exports at full resolution with no watermark, and adds the colour looks, the extra controls, the build-up video and an unlimited gallery. Google Play handles all payment; the app never sees or stores payment details. Permissions used: CAMERA (required for its core purpose — reading frames to build the exposure), INTERNET (used ONLY for two things: Google Play Billing, and fetching a small remote configuration file from the developer's own server that carries feature flags such as whether the subscription is on sale and a maintenance notice), and WAKE_LOCK (to keep the screen awake during long exposures, which can run for minutes; if the screen slept the capture would end).