# Planet Gravity vs SkyLetter

The clearest difference is update cadence: SkyLetter at fortnightly against Planet Gravity's every 14 months. SkyLetter also leads on iOS requirement (12.0 vs 17.6). On price, review sentiment, ads and in-app purchases there is nothing between them.

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

Planet Gravity ships an update every 14 months, SkyLetter fortnightly. The most recent releases landed on October 6, 2026 and October 23, 2026 respectively.

## The numbers

| Metric | Planet Gravity | SkyLetter |
| --- | --- | --- |
| Price | Free | Free |
| Rating | — | **[1.0 (1 ratings)](https://appshunter.io/ios/app/skyletter/id1469768088/reviews)** |
| Number of ratings | — | **1** |
| Positive reviews | 25.0% of reviews | 25.0% of reviews |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 14 months | **Fortnightly** |
| Monetization | Free | Free |
| Size | 5 MB | 45 MB |
| Requires iOS | 17.6 | **12.0** |
| Devices | iPhone, iPad | iPhone, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Niagara Mobile LLC](https://appshunter.io/developer/1039399999) | [Kiyotaka Watanabe](https://appshunter.io/developer/1408976233) |

## What reviewers say

### Planet Gravity

[App page](https://appshunter.io/ios/app/planet-gravity/id995682820)

Explore the gravitational pull of different celestial bodies. Watch pendulums swing and collide under varying gravitational forces, offering a unique physics simulation experience.

**Highlights:** Select different planets for unique gravity, Observe pendulum collisions, Physics-based simulation, Educational planet facts, Interactive entertainment

**Features:** macOS Compatibility

**In-app purchases:** none


### SkyLetter

[App page](https://appshunter.io/ios/app/skyletter/id1469768088)

Create personalized messages drawn in the sky with airplane contrails. Share your creations as videos or photos on social media, perfect for sending unique greetings or declarations.

**Highlights:** Draw messages in the sky with contrails, Share creations as video or photo, Personalize messages for friends, Unique social media content

**Features:** macOS Compatibility

**In-app purchases:** none


## Frequently asked questions

### Is Planet Gravity free?

Planet Gravity is free to download, with no in-app purchases.

### Is SkyLetter free?

SkyLetter is free to download, with no in-app purchases.

### Do Planet Gravity or SkyLetter have ads?

Neither Planet Gravity nor SkyLetter shows ads.

### Which is updated more often, Planet Gravity or SkyLetter?

Planet Gravity ships an update every 14 months, and SkyLetter fortnightly. Most recently, Planet Gravity was updated on October 6, 2026 and SkyLetter on October 23, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*