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.
5 Stars
$1.99 · In-app purchases
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.
A product spec, screen plans, and build steps for your coding agent.
First kit free with a verified email
Combine features and design from your favorite apps.
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Generating… usually about a minute.
What should your app do differently? Your note travels with the kit so your coding agent builds around your idea.
A product spec, phased build plan, differentiation notes, and screen references.
Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Goal: Send a clear invoice after finishing a job.
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.
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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Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
Rork plan preview for Calc-12E RPN Financial: map the core Business workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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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
Assumption to check: Limited advanced functions compared to competitors
Validate with people who use this workflow before building.
Hypothesis 2
Assumption to check: No cloud sync for history
Validate with people who use this workflow before building.
Hypothesis 3
Assumption to check: User interface feels outdated
Validate with people who use this workflow before building.
Hypothesis 4
Assumption to check: No tutorial or help section
Validate with people who use this workflow before building.
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
5 Stars. “I can't tell you how often I use it, probably about as much as the phone app!" - CharlieW, President. Waterman & Company (Real Estate Investment and Development) “This is the first 12C type calculator for the itouch that has actually made me put down my real 12C. One of the best features of this calculator is the register display where you can see what is in FV, I, PV, PMT, etc. That alone makes it worth the $14.95 price. Consider the many other features that it has over and above the real 12C and you have one sweet program here. Best of the 12C emulators out there - hands down! “ - tsinvest It started in early 2008 with a belief that: • there was one and only one insanely great financial calculator • the iPhone is the perfect platform to bring that calculator back to life • it's not good enough to just copy the old, you have to make it better • a financial calculator is a professional tool, not a game From this mindset came Calc-12E, the first 12C emulator on the App Store. It was expensive back then ($20-$25) and compared to a game it still is because, well, you usually get what you pay for. Specifically: Foremost, if the math isn't right in the corner cases I can't trust the calculator. Calc-12E's algorithms were written for iOS by a (the?) key member of the original 12C development team who incorporated his solutions to the quirks in financial computation that historically tripped up lesser implementations. There are reasons the 12C was the absolute best, and Calc-12E draws directly on that heritage. While the original did what it could, 1980s technology made many features difficult, impractical or impossible to use. Calc-12E pioneered the following innovations to address shortcomings: • you can always see what's in the financial registers (and stack if you choose) so you have instant assurance that you've entered your data correctly. This feature has been copied by nearly every emulator on the App Store, for good reason. • visual cash flow editing radically eases how you deal with cash flows... believe it or not it is actually easy to manipulate cash flows with Calc-12E. There's a demo on YouTube, search for Calc12E. • Investment mode allows you to simultaneously evaluate metrics on up to three cash flow scenarios at a time. You can compare cash flows side-by-side AND because of visual cash flow editing you can play what-if games • the results of some calculations need to "leave the phone" to be useful. Amortization schedules, leasing terms, bond yields... everything can be sent via email using customizable templates Finally, a professional tool receives continuing support and updates. It does not nag you to rate it, it does not invite you to pay to get more. It does not crash. Check out Calc-12E's version history and reviews of previous versions. This is a live, supported app with tens of thousands of long term customers and I have never charged for an upgrade or cloaked features behind ads or paywalls. It's not ethical at this level (in my humble opinion!). When you buy Calc-12E you get my best (and evolving!) rendition of the most popular handheld calculator ever made. It's core (the math) comes from the same mind as your trusty original and to that foundation you get usability advances that actually enhance the overall tool.
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Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
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.