RxMarbles vs 21 Sharp
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
RxMarbles
Visualize and understand ReactiveX observable sequences with interactive diagrams. This educational tool helps developers grasp complex asynchronous programming concepts by illustrating event-based data streams and composition operators.
- Interactive observable diagrams
- Visualization of event streams
- Demonstration of composition operators
- Educational tool for asynchronous programming
- Explains observer pattern extensions
Read full descriptionHide full description
Interactive diagrams of Rx Observables. ReactiveX is a library for composing asynchronous and event-based programs by using observable sequences. It extends the observer pattern to support sequences of data and/or events and adds operators that allow you to compose sequences together declaratively while abstracting away concerns about things like low-level threading, synchronization, thread-safety, concurrent data structures, and non-blocking I/O.
21 Sharp
Master blackjack strategy and card counting with this professional-grade trainer. Learn optimal plays, practice counting systems, and track your progress with realistic simulations and reference guides. Reduce the house edge and gain a competitive advantage.
- Basic strategy training
- Card counting drills (Hi-Lo)
- Realistic practice table
- Reference guides
- Progress tracking and achievements
Read full descriptionHide full description
Turn the odds in your favor. 21 Sharp is a professional-grade blackjack trainer that teaches you basic strategy and card counting—the same techniques used by advantage players to beat the house. BASIC STRATEGY TRAINING Learn the mathematically optimal play for every possible hand. Our quiz system drills you on 270+ hand combinations until perfect strategy becomes second nature. Reduce the house edge to just 0.5%. CARD COUNTING DRILLS Master the Hi-Lo counting system with speed-building exercises. Track running counts, calculate true counts, and learn when to increase your bets. Practice until you can count down a full shoe with accuracy. PRACTICE TABLE Play realistic blackjack hands with real-time strategy hints. See the running count, get recommendations for every decision, and learn from your mistakes without risking real money. REFERENCE GUIDES Access complete basic strategy charts and a comprehensive Hi-Lo counting guide anytime. Perfect for quick review before hitting the casino. TRACK YOUR PROGRESS Unlock 25+ achievements as you improve. Monitor your accuracy, streaks, and stats across all training modes. Watch yourself transform from beginner to sharp. Whether you're preparing for Vegas, want to impress at home games, or just love the math behind the game, 21 Sharp gives you the edge. Play Sharp. Win Sharp.
Screenshots
Verdict
The clearest difference is in-app purchases: RxMarbles at none against 21 Sharp's 1. RxMarbles also leads on ratings volume (16 vs 1) and iOS requirement (9.2 vs 17.0). On price, rating, ads and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. 21 Sharp sells 1 one-off in-app purchase. RxMarbles asks for nothing beyond the download.
On the App Store both sit at effectively the same score — 4.9 for RxMarbles against 5.0 for 21 Sharp. That said, the two scores are not equally well evidenced: RxMarbles has 16 ratings behind it against 1, so its average is the more settled of the two.
| Parameter | RxMarbles | 21 Sharp |
|---|---|---|
| Price | Free | Free |
| Rating | 4.9 (16 ratings) | 5.0 (1 ratings) — better |
| Positive reviews | 84.0% of reviews | — |
| Number of ratings | 16 — better | 1 |
| Update frequency | Every 4 months | — |
| Ads | No | No |
| In-app purchases | No — better | Yes |
| Monetization | Free — better | Free with in-app purchases |
| Devices | iPhone, iPad, iPod — better | iPhone, iPad |
| Requires iOS | 9.2 — better | 17.0 |
| Further details — not scored | ||
| Size | 21 MB | 1 MB |
| Age rating | 4+ | 12+ |
| Developer | AnjLab | busyslacker llc |
Customer experience
RxMarbles
21 Sharp
In-app purchases
RxMarbles
No in-app purchases
21 Sharp
- 21 Sharp Premium$2.99









