# 知了单词书 vs OpenFlat

The clearest difference is update cadence: 知了单词书 at every 5 days against OpenFlat's every 2 weeks. On price, ads, in-app purchases and device support there is nothing between them.

Both are free to download. 知了单词书 sells 1 one-off in-app purchase and OpenFlat sells 10 in-app purchases, starting at $49.99 per month. Whichever you choose, the download price is not the number that matters.

知了单词书 ships an update every 5 days, OpenFlat every 2 weeks. The most recent releases landed on September 19, 2026 and September 13, 2026 respectively.

## The numbers

| Metric | 知了单词书 | OpenFlat |
| --- | --- | --- |
| Price | Free | Free |
| Rating | — | **[5.0 (2 ratings)](https://appshunter.io/ios/app/openflat/id6756606310/reviews)** |
| Number of ratings | — | **2** |
| In-app purchases | Yes | Yes |
| Ads | No | No |
| Update frequency | **Every 5 days** | Every 2 weeks |
| Monetization | — | Free with in-app purchases |
| Size | 63 MB | 81 MB |
| Requires iOS | **12.0** | 13.0 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 17+ | 4+ |
| Developer | [重庆知竣文化传媒有限公司](https://appshunter.io/developer/1814794912) | [柳 杨](https://appshunter.io/developer/1734826226) |

## What reviewers say

### 知了单词书

[App page](https://appshunter.io/ios/app/id6746037035)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| 知了1年会员 | $39.99 | one-time |


### OpenFlat

[App page](https://appshunter.io/ios/app/openflat/id6756606310)

This app provides an online teaching platform for individual instructors, featuring interactive whiteboards, audio/video communication, presentation tools, and recording capabilities. Users can easily join, create, and schedule virtual classrooms. It aims to be the preferred tool for online educators.

**Highlights:** Multi-person online whiteboard, Audio and video communication, PPT presentation with animations, Room recording and playback, Screen sharing, Room creation, joining, and scheduling

**In-app purchases (10)**

| Purchase | Price | Billing |
| --- | --- | --- |
| OpenFlat 高级版连续包月 | $49.99 | per month |
| OpenFlat 基础版连续包年 | $79.99 | per year |
| OpenFlat 课次购买 | $0.99 | one-time |
| OpenFlat 基础版一个月 | $6.99 | one-time |
| OpenFlat 专业版一个月 | $22.99 | one-time |
| OpenFlat 高级版一个月 | $49.99 | one-time |
| OpenFlat 基础版十二个月 | $79.99 | one-time |
| OpenFlat 专业版十二个月 | $249.99 | one-time |
| OpenFlat 高级版十二个月 | $599.99 | one-time |
| OpenFlat 畅享版 | $900.00 | one-time |


## Frequently asked questions

### Is 知了单词书 free?

知了单词书 is free to download, with in-app purchases available.

### Is OpenFlat free?

OpenFlat is free to download, with in-app purchases available.

### Do 知了单词书 or OpenFlat have ads?

Neither 知了单词书 nor OpenFlat shows ads.

### Which is updated more often, 知了单词书 or OpenFlat?

知了单词书 ships an update every 5 days, and OpenFlat every 2 weeks. Most recently, 知了单词书 was updated on September 19, 2026 and OpenFlat on September 13, 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.*