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
TailFin
TailFin is a Wii U (8th generation console) emulator for iPhone and iPad, built on Cemu
$1.99 · In-app purchases
PRICE
$1.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.4
5 ratings · Top 30%
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.
Build your own version
Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
What's included15 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
Preview a sample Build Kit No email needed
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 TailFin: map the core Entertainment 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
Introduce more diverse games and interactive community features.
Assumption to check: Limited game variety and engagement
Validate with people who use this workflow before building.
Hypothesis 2
Create a guided onboarding for new users to navigate easily.
Assumption to check: Poor onboarding experience
Validate with people who use this workflow before building.
Hypothesis 3
Add friend systems and leaderboards for competition.
Assumption to check: Lack of social features
Validate with people who use this workflow before building.
Hypothesis 4
Implement more in-app purchase options and subscription models.
Assumption to check: Insufficient monetization options
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
TailFin is a Wii U (8th generation console) emulator for iPhone and iPad, built on Cemu. Load your own games, manage your library, and play with touch controls or a gamepad. Browse your library in console mode with a gamepad-friendly carousel and full controller navigation. AirPlay to a TV or monitor and play on the big screen while your iPhone or iPad stays the GamePad. Tune game speed from 50% to 800%, or run unlimited when you want to skip slow sections or need an extra boost! Switch between TV and GamePad views, apply community made graphic packs, and import Amiibo or emulate Skylander portal! Supported formats include WUD, WUX, RPX, and ELF. Add games from the library or Share to TailFin. You need your own keys and system files for encrypted titles. Features: • AirPlay TV play with phone as GamePad JUST LIKE REAL HARDWARE • Console-style library with gamepad navigation • Adjustable game speed up to 800% • native renderer • Full controllers with haptics and rumble • Customizable on-screen GamePad layout • TV and GamePad view switching on instantly • Amiibo support (.bin dumps) • Graphic packs & Mods • Customizable HUD (FPS, GPU, CPU, RAM & more!) • Fully Customizable UI & themes TailFin is not affiliated with Nintendo or the Cemu project. Wii U and Nintendo are trademarks of Nintendo Co., Ltd. Use only game data you are legally entitled to run.
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
Supabase
React Navigation
Zustand
React Native Reanimated
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.
