# 知识树 vs 21天突破高频词汇

The clearest difference is price: 知识树 at Free against 21天突破高频词汇's $0.99. 知识树 also leads on update cadence (every 5 days vs every 3 weeks). 21天突破高频词汇's advantage is in-app purchases (none vs 4). On ads, device support and iOS requirement there is nothing between them.

知识树 is free to download; 21天突破高频词汇 costs $0.99 up front. 知识树 sells 4 in-app purchases, starting at $2.99 per month. 21天突破高频词汇 asks for nothing beyond the download.

知识树 ships an update every 5 days, 21天突破高频词汇 every 3 weeks. The most recent releases landed on October 6, 2026 and October 8, 2026 respectively.

## The numbers

| Metric | 知识树 | 21天突破高频词汇 |
| --- | --- | --- |
| Price | **Free** | $0.99 |
| Rating | **[4.2 (5 ratings)](https://appshunter.io/ios/app/ai/id6505133670/reviews)** | — |
| Number of ratings | **5** | — |
| Positive reviews | 38.9% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Every 5 days** | Every 3 weeks |
| Monetization | Freemium | — |
| Size | 2 MB | 3 MB |
| Requires iOS | 17.0 | 17.0 |
| Devices | **iPhone, iPad** | iPhone |
| Age rating | 4+ | 4+ |
| Developer | [野 匡](https://appshunter.io/developer/819954894) | [鲁扬 王](https://appshunter.io/developer/1890054449) |

## What reviewers say

### 知识树

[App page](https://appshunter.io/ios/app/ai/id6505133670)

This intelligent learning system uses AI to understand knowledge, break down concepts, and dynamically schedule practice and review based on your memory state. It focuses on true retention through spaced repetition and scientific memory curves, not just completing exercises.

**Highlights:** AI-driven knowledge understanding, Dynamic practice and review scheduling, Breakdown of knowledge into testable points, Spaced repetition for long-term memory, Automatic assessment of mastery, Progress tracking over speed

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

**In-app purchases (4)**

| Purchase | Price | Billing |
| --- | --- | --- |
| 月度会员 | $2.99 | per month |
| 季度会员 | $4.99 | per 3 months |
| 年度会员 | $19.99 | per year |
| 终身会员 | $24.99 | one-time |


### 21天突破高频词汇

[App page](https://appshunter.io/ios/app/21/id6797169848)

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

**In-app purchases:** none


## Frequently asked questions

### Is 知识树 free?

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

### Is 21天突破高频词汇 free?

21天突破高频词汇 costs $0.99, with no in-app purchases.

### Do 知识树 or 21天突破高频词汇 have ads?

Neither 知识树 nor 21天突破高频词汇 shows ads.

### Which is updated more often, 知识树 or 21天突破高频词汇?

知识树 ships an update every 5 days, and 21天突破高频词汇 every 3 weeks. Most recently, 知识树 was updated on October 6, 2026 and 21天突破高频词汇 on October 8, 2026.

---

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