Nine Questions

One brutal puzzle a day. Sharpen your brain in minutes.

Turn abstract probability and statistics concepts into visible, easy-to-understand content with fun interactive visual demos. Master core probabilistic thinking, and dive deep into classic theories including the Law of Large Numbers, Bayes' Theorem,

自动识别公开牌面、追踪剩余牌，支持斗地主、跑得快、掼蛋，提供 iOS 与 Android 版本。

Simple online tests for reaction time, memory, and focus

cpstest is a web-based tool for testing mouse click speed, evaluating concentration, measuring reaction speed, and providing fun, focused training.

A family learning companion that turns daily effort into growth