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
EvilTwin
Evil Twin is a creative stereo processing effect designed to add width, motion, depth, and unexpected character to your sound.
$2.99 · In-app purchases
PRICE
$2.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 5.0
1 ratings · Top 5%
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 included13 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 EvilTwin: map the core Music 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
Implement more personalized recommendations and trending music sections.
Assumption to check: Limited music discovery features compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Add options for users to share playlists and tracks on social media.
Assumption to check: Lack of social sharing features
Validate with people who use this workflow before building.
Hypothesis 3
Improve offline caching mechanisms to ensure a smoother experience.
Assumption to check: Inconsistent offline playback quality
Validate with people who use this workflow before building.
Hypothesis 4
Simplify onboarding and provide tooltips for first-time users.
Assumption to check: Complex navigation flow for new users
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
Evil Twin is a creative stereo processing effect designed to add width, motion, depth, and unexpected character to your sound. Built for musicians, producers, sound designers, and experimental artists, Evil Twin combines stereo enhancement with controlled instability, allowing you to move from subtle spatial polish to dramatic transformations with a simple and focused interface. Whether you're widening a synth, adding movement to a pad, creating animated textures, or pushing sounds into unfamiliar territory, Evil Twin encourages exploration while remaining fast and musical to use. Features: • Creative stereo enhancement and widening • Dynamic movement and spatial animation • Subtle-to-extreme sound shaping possibilities • Simple, performance-focused interface • AUv3 support for iPad and Mac • Works in compatible hosts including GarageBand, Logic Pro, AUM, Cubasis, and Audiobus Evil Twin is designed for creators who enjoy discovering new sounds rather than following predictable presets. Sometimes the best results happen when things drift a little off course. Basic usage guide at folinaaudio.com.
Written user reviews are not shown here. Check current App Store reviews >
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
Zustand
Axios
@react-navigation/native
expo-av
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.
