Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
App Overview
Train Kit
Hop on board! Train Kit lets you build immersive little train worlds.
$6.99 · In-app purchases
PRICE
$6.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.6
2,350 ratings · Top 15%
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What's included17 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
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Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Differentiate and validate
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Free quick prompt For a smaller starting point
Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Train Kit: map the core Education workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Offer a broader range of topics and expert instructors.
Assumption to check: Limited course content variety.
Validate with people who use this workflow before building.
Hypothesis 2
Implement offline downloads for course materials.
Assumption to check: No offline access for courses.
Validate with people who use this workflow before building.
Hypothesis 3
Add forums or discussion boards for users to connect.
Assumption to check: Lack of community features.
Validate with people who use this workflow before building.
Hypothesis 4
Simplify the paywall and clarify subscription tiers.
Assumption to check: In-app purchases can be confusing.
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
Hop on board! Train Kit lets you build immersive little train worlds. EASY TO BUILD Simply add and move track tiles by dragging them with your finger while trains run around you. There’s no need to switch between modes – everything is on one screen. GET CREATIVE No rules, but endless options. Add trains, tunnels, junctions and scenery in a totally open-ended world. 3D Immerse yourself in a fully 3D world. You can even put yourself in the driver’s seat and see what it’s like to drive around your track from the train’s cabin. FEATURES - Add track tiles which snap together in a grid - Tunnels and bridges - Switching tracks allow your trains to take different routes - Drop trains and carriages onto your track - Create your own unique train by mixing carriages together - Simple train controls allow you speed up, slow down or reverse your trains - Adding scenery and building objects brings your world to life - Train driver view allows you to whizz through your world - No in-app purchases - No adverts
Written user reviews are not shown here. Check current App Store reviews >
Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
SUGGESTED BUILD STACK
React Native
Expo
React Navigation
Axios
React Native Video
Zustand
BUILD KIT DIFFICULTY
Advanced
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.
