# STACK999

> Reverse Polish notation (RPN) stack calculator for iOS devices. (iPhone/iPad app by Manabu Fukui.)

- Source: https://appshunter.io/ios/app/stack999/id382001084 (this page in markdown: same URL + `.md`)
- Developer: [Manabu Fukui](https://appshunter.io/developer/360698288)
- Category: Utilities, Education
- Price: Free
- Rating: 4.00/5 from 1 App Store ratings · 3 written reviews indexed
- Age rating: 4+
- Requires: iOS 13.0 · 1 MB
- Languages: American English
- Released: 2010-07-20
- Data updated: 2026-06-10
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/stack999/id382001084/reviews.md

## What is STACK999?

STACK999 is the stack calculator.
 (Reverse Polish notation calculator)

## Key features

- Reverse Polish Notation (RPN) input
- Stack-based calculations
- Calculator utility

## Recent user reviews (3 of 3)

All indexed reviews: https://appshunter.io/ios/app/stack999/id382001084/reviews.md

### 5/5 — Perfect app!

*2017-01-08, version 2.0.1*

This app is great! I wanted an RPN calculator that looked nice, and was free, and this was it! Has all the needed functions, a nice long stack, and is elegant and utilitarian. Perfect. I would have loved a way to paste in numbers, but I might just be missing how you're supposed to do that. And maybe a few more esoteric functions for fun, but over all this is the only good RPN calculator I've ever found for iOS.

### 5/5 — Simple but great

*2011-10-30, version 0.1*

This is the best of the free rpn calculators I have found. I actually like the while minimal gui. Plus is has all the trig, log, and power functions you really need. Great app!
Thank you for providing a fully functional rpn calculator for free!

### 5/5 — Great little app

*2011-03-27, version 0.1*

I use an hp32 - but this little app for my iPod touch is very cool and very handy

## Frequently asked questions about STACK999

### What is STACK999?

STACK999 is a calculator application that utilizes Reverse Polish Notation (RPN) for input and calculations. This method uses a stack to manage numbers and operations.

### Is STACK999 free to use?

Yes, STACK999 is available for free. It was released on July 20, 2010, and is offered at no cost to users.

### What devices support STACK999?

STACK999 is compatible with iPhone, iPad, and iPod devices. It is designed for the iOS ecosystem.

### What is the age rating for STACK999?

STACK999 has an age rating of 4+. This indicates it is suitable for children and adults.

### How often is STACK999 updated?

The latest version of STACK999, 2.3.2, was released on October 15, 2019. Updates are not frequent, with the last update being several years ago.

### What is the user rating for STACK999?

STACK999 has a rating of 4.0 stars based on a single review. This indicates a generally positive reception from its limited user base.

### Does STACK999 have ads?

The provided data does not specify if STACK999 contains advertisements. As it is a free utility app, it may or may not include ads.

## Version history (last 5 releases)

### 2.3.2 — 2019-10-15

Large Text Support.
Improve button panel.

### 2.3.1 — 2019-10-02

bug fix

### 2.3 — 2019-09-25

iOS13(Dark Mode) Support.

### 2.2 — 2018-11-20

iPhoneX(notch) Support.
iOS12 Support.
Undo Support.
Key Pressed Sound.

### 2.1 — 2017-04-24

Add "Paste" support

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## More apps by Manabu Fukui

- [IRC999A](https://appshunter.io/ios/app/irc999a/id800798888)
- [MORSE999](https://appshunter.io/ios/app/morse999/id806725036)
- [CASL999](https://appshunter.io/ios/app/casl999/id1046352877)
- [SORO999](https://appshunter.io/ios/app/soro999/id1229427336)
- [CODE999](https://appshunter.io/ios/app/code999/id1258682642)

All apps by Manabu Fukui: https://appshunter.io/developer/360698288

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-06-10.*