The App "Reaction Training" is not maintained any more. Instead, it had been merged in a new App named "葦遊小境". You can download it in the following page:
https://play.google.com/store/apps/details?id=com.blogspot.karryapps.karrygames
Since the new App does not has English user interface. Here is a guide for English player to play "Reaction Training" in this new App.
When the first time you enter this app, there are some boring things must to do. Thank you for taking your patience to finish it.
After you download and open it, you can see this page.
Please input you player name in the input box and hit the blue button. Then, you will get the following page. Next time when you enter this app, you will see this page without introduction any more.
Hit the second button in the bottom-left corner as marked by a red box in the image above. You will see the following page:
Here is a list of some little games that this App provided. As you see, there is a button with the same icon with "Reaction Training". That is our target. But before continue to talk about it, I want to say you may also like to play the other games in this list ─ except the third one due to it depends on idioms of Chinese language. They are also simple to play even if without English user interface. I hope you could try them and like them, too.
Let's back to "Reaction Training". Hit the button as marked by a red box in the image above. It will show a list.
Same with the "Reaction Training" app, there are several mode can be play. Hit one you want to play or try them all. After you hit one, you will see a page like this:
The popup is also a simple introduction of that mode of "Reaction Training". Hit the blue button to close it.
Now you can hit the button in bottom-right corner to start to play.
I hope you will also like it in this new app. Thank you!