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
Retromulator
Retromulator is a multi-core retro hardware emulation app and AUv3 plug-in that brings legendary synthesizer, sampler, and keyboard cores back to life through authentic low-level emulation
$4.99 · In-app purchases
PRICE
$4.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 3.0
2 ratings · Below Average
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 included14 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 Retromulator: 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
Expand synth offerings and regularly update with new sounds.
Assumption to check: Limited instrument variety compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Streamline UI elements for better usability.
Assumption to check: User interface feels cluttered
Validate with people who use this workflow before building.
Hypothesis 3
Focus on user feedback to improve functionality and performance.
Assumption to check: 3.0 rating indicates dissatisfaction
Validate with people who use this workflow before building.
Hypothesis 4
Simplify the purchasing process and clearly communicate benefits.
Assumption to check: In-app purchase complexity
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
Retromulator is a multi-core retro hardware emulation app and AUv3 plug-in that brings legendary synthesizer, sampler, and keyboard cores back to life through authentic low-level emulation. Each core runs its actual firmware, physical model, or sample data — delivering the unmistakable character of the hardware that defined electronic music from the early 80s through the 2000s. EMULATED CORES Virtual Analog Synths (Motorola DSP 56300 recreation, interpreter mode) — built on the open-source Gearmulator by the dsp56300 team: DISCLAIMER: Apple's iOS App Store does not allow Just-In-Time (JIT) code generation in third-party apps. As a result, the DSP 56300 cores run in pure interpreter mode, which is significantly slower than the desktop JIT version. Expect higher CPU usage, reduced polyphony, and limited multitimbral capability compared to the desktop edition. A modern device (A14 / M1 or newer) is recommended for the DSP-based cores. Even on an M1 / A16-class chip, a high audio buffer size (high-latency setting) is required and polyphony remains very limited — these cores are not intended for low-latency live performance on iOS. • Access Virus A, B and C • Access Virus TI / TI2 / Snow • Clavia Nord Lead 2X • Roland JP-8000 • Waldorf microQ • Waldorf Microwave XT FM Synthesis: • Yamaha DX7 — original chip set emulation, based on VDX7 by Charles Chiaccona • Yamaha OPL3 — Nuked OPL3 cycle-accurate FM by Nuke.YKT Electric Piano and Sampler: • Wurlitzer 200A — OpenWurli physical modelling by hal0zer0 (Rust ported to C++ by discoDSP) • Akai S1000 — SFZero sample engine by Steve Folta, with Bliss Sampler support and resampling engine by discoDSP (SF2 / SFZ / ZBP / ZBB) KEY FEATURES • Native AUv3 plug-in for AUM, Cubasis, GarageBand, Logic Pro and more • Standalone app for iPhone and iPad • Full MIDI control: CC, mod wheel, expression, pitch bend • 8-point sinc interpolation for sample playback • Auto-slice drum mapping and global retuning via MIDI • ROM firmware loading from original hardware • Background audio, iCloud and Files app integration • Optimised JIT-less interpreter compatible with iOS App Store sandbox
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
React Navigation
expo-av
react-native-reanimated
BUILD KIT DIFFICULTY
Expert
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.
