A "reacto" is a small token / piece of code that can be embedded into any text to give it the power to update itself dynamically. Thus a "reacto" turns a normal text into a dynamic text or a reactive text. The term "reacto" was made as a 'short' from "reactive token".
Reactos can be used while writing stories / tales in the new-age dynamic story writing platform Reactale to give your tales reactive abilities and come to life.
There are various to get started with reactos,