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
Nulltrack
Launch price $4.99 — rises to $7.99 four weeks after release
$4.99
PRICE
$4.99
No in-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
N/A
No ratings yet
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 included15 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 Nulltrack: 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
Focus on unique music recommendations based on user preferences.
Assumption to check: Limited music library compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Implement offline downloads for all tracks.
Assumption to check: Lack of offline playback feature
Validate with people who use this workflow before building.
Hypothesis 3
Add features for sharing music with friends through social media.
Assumption to check: No social sharing capabilities
Validate with people who use this workflow before building.
Hypothesis 4
Create a guided onboarding process to help users set preferences.
Assumption to check: Poor user onboarding experience
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
Launch price $4.99 — rises to $7.99 four weeks after release. Get it early! Nulltrack! It's null when you start and a track when you finish! Nulltrack is a tracker and digital audio workstation app for your phone. A different way to make music inspired by LSDJ and the Dirtywave M8. Features: AUv3 plugin support - bring your external synths and effects into your track! Two built-in synthesizers -- A versatile two-oscillator Basic Synth and a feature-rich Bass Synth. A built-in sampler -- record your own samples with your phone's microphone, load your own, or use the built-in samples, set loop points, slice, reverse, etc. Modulation -- Modulate nearly anything with LFOs, AHD / ADSR / drum envelopes, velocity, randomness, and key tracking, filter, panning, and more. Mixing Features -- track faders with solo and mute, 13 built-in effects, sidechain compression Sends -- share effects between tracks Customize your swing/playback with groove tables! Lock your patterns to a built-in scale! ...and much more! New to trackers? They're a fast, grid-based way to write music. Try it out! No ads, no subscription, no in-app-purchases, and no account needed.
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
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Axios
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.
