Price 45$ on Unity Asset Store: https://assetstore.unity.com/packages/tools/visual-scripting/react-516
But now you can download React FREE.
React is a Behaviour Tree tool which can add intelligent behaviour to your game objects. It makes things as simple as possible for the game designer, yet remains very powerful for the game programmer.
It feature zero runtime memory allocation, and zero runtime reflection. It is fast, lean and efficient. Adding your own classes as nodes in the tree is as simple as as adding a [ReactExpose] attribute, code generation then takes over!
unityassetcollection.com – Get all paid Unity Asset for free