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
Blackstone Unlimited
Never wait to check out an audiobook again— your library card ensures you’re always first in line!
Free
PRICE
Free
No in-app purchases
BUSINESS MODEL
Free
No overall Grossing estimate available
RATING
★ 4.3
630 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.
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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 should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
What's included
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 Blackstone Unlimited: map the core Books 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 better caching and offline storage features.
Assumption to check: Limited offline access to audiobooks
Validate with people who use this workflow before building.
Hypothesis 2
Use machine learning algorithms to enhance recommendation system.
Assumption to check: Lack of personalized recommendations
Validate with people who use this workflow before building.
Hypothesis 3
Allow users to share their favorite audiobooks on social media.
Assumption to check: No social sharing options
Validate with people who use this workflow before building.
Hypothesis 4
Enhance search with filters and advanced options.
Assumption to check: Poor search functionality
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
Never wait to check out an audiobook again— your library card ensures you’re always first in line! Welcome to Blackstone Unlimited, a digital library platform. Borrow bestselling audiobooks for free with your library card and listen anytime, anywhere. Our award-winning catalog is available to you instantly with no holds or waiting. With over 7,000 titles to choose from and fresh new arrivals coming in regularly, you’re sure to find the perfect listen for every mood. Contact your local library today to see if they participate in the Blackstone Unlimited program. Getting set up is quick and easy. Our login and sign-up process is easier than ever with passwordless login— more secure, faster, and free of the hassle of remembering passwords. Don’t let a lack of WiFi get in the way of your plans! Download audiobooks for listening on the go.
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
expo-av
Zustand
BUILD KIT DIFFICULTY
Not assessed in a Build Kit yet.
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.
